HOW CROPS FEED. 

^ //jv,J\ A TREATISE ON THE 

ATMOSPHERE AND THE SOIL 

AS EELATED TO THE 

Nutrition of Agrioulturai Plants. 

WITH ILLUSTRATIONS. 



SAMUEL W. JOHNSON-, M.A., 

PEOFKSSOR OP ANALYTICAL AND AGRICTJLTTTRAL CHEMISTKY IN THE SHEFFIELD 
SCIENTIFIC SCHOOL OF YALE COLLEGE ; CHEMIST TO THE CONNEC- 
TICUT STATE AGEICULTUEAL SOCIETY ; MEMBER OF THE 
NATIONAL ACADEMY ^F, SCIENCES. 



'H 



<k 



\ 
NEW YORK; 



ORANGE JUDD AND COMPANY, 

R 

/ 



245 BROADWAY. 

I- , ■■-■ 



Qy 



Entered according to Act of Congress, in the year 1870, by 
ORANGE JUDD & CO., 

In the Clerk's Oflace of the District Court of the United States for the Southern 
District of New York, 



PREFACE. 



The work entitled " How Crops Grow " has been re- 
ceived with favor beyond its merits, not only in America, 
but in Europe. It has been republished in England under 
the joint Editorship of Professors Church and Dyer, of 
the Royal Agricultural College, at Cirencester, and a 
translation into German is soon to appear, at the instiga- 
tion of Professor von Liebig. 

The Author, therefore, puts forth this volume — the com- 
panion and complement to the former — with the hope that 
it also will be welcomed by those who appreciate the sci- 
entific aspects of Agriculture, and are persuaded that a 
true Theory is the surest guide to a successful Practice. 

The writer does not flatter himself that he has produced 
a popular book. He has not sought to excite the imagi- 
nation with high- wrought pictures of overflowing fertility 
as the immediate result of scientific discussion or experi- 
ment, nor has he attempted to make a show of revolution- 
izing his subject by bold or striking speculations. His 
ofiice has been to digest the cumbrous mass of evidence, 

in which the truths of Vegetable Nutrition lie buried out 
5 



VI PEEFACE. 

of the reach of the ordinary inquirer, and to set them 
forth in proper order and in plain dress for their legiti- 
mate and sober uses. 

It has cost the Investigator severe study and labor to 
discover the laws and many of the facts which are laid 
down in the following pages. It has cost the Author no 
little work to collect and arrange the facts, and develop 
their mutual bearings, and the Reader must pay a similar 
price if he would apprehend them in their true signifi- 
cance. 

In this, as in the preceding volume, the Author's method 
has been to bring forth all accessible facts, to present their 
evidence on the topics under discussion, and dispassion- 
ately to record their verdict. If this procedure be some- 
times tedious, it is always safe, and there is no other mode 
of treating a subject which can satisfy the earnest inquirer. 

It is, then, to the Students of Agriculture, whether on the 
Farm or in the School, that the Author commends his 
book, in confidence of receiving full sympathy for its 
spirit, whatever may be the defects in its execution. 



CONTENTS. 



Introductiok 17 

DIVISION I. 

THE ATMOSPHERE AS RELATED TO VEGETATION. 

CHAPTER I. 

Atmospheric Air as the Food of Plants. 

§ 1. Chemical Composition of the Atmosphere 21 

§ 2. Relation of Oxygen Gas to Vegetable Nutrition ; . . .22 

§ 3. " " Nitrogen Gas to " " 26 

§ 4. " " Atmospheric Water to Vegetable Nutrition 34 

§ 5. " " Carbonic Acid Gas " " " 38 

§6. I 'I Atmospheric Ammonia to " " 49 

§ 7. Ozone 63 

§ 8. Compounds of Nitrogen and Oxygen in the Atmosphere 70 

§ 9. Other Ingredients of the Atmosphere 91 

§ 10. Recapitulation of the Atmospheric Supplies of Food to Crops 94 

§ 11. Assimilation of Atmospheric Food 97 

§ 12. Tabular View of the Relations of the Atmospheric Ingredients to the 
Life of Plants 98 

CHAPTER II. 

The Atmosphere as Physically Related to Vegetation. 

§ 1. Manner of Absorption of Gaseous Food by Plants 99 

DIVISION II. 

THE SOIL AS RELATED TO VEGETABLE PRODUCTION. 

CHAPTER I. 

Introductory 104 

7 



VIII HOW CKOPS FEED. 

CHAPTEK II. 
Origin and Formation op Soils 106 

§ 1. Chemical Elements of Rocks 107 

§ 2. Mineralogical Elements of Rocks 108 

§ 3. Rocks, their Kinds and Characters, 117 

§ 4. Conversion of Rocks into Soil 122 

§ 5. Incorporation of Organic Matter with the Soil, and its Effects 135 

CHAPTER III. 
Kinds of Soils, their Definition and Classification. 

§ 1. Distinctions of Soils based upon the Mode of their Formation or Deposi- 
tion 142 

§ 2. Distinctions of Soils based upon Obvious or External Characters 140 

CHAPTER IV. 

Physical Characters of the Soil 157 

§ 1. Weight of Soils 158 

§ 2. State of Division 159 

§ 3. Absorption of Vapor of Water 161 

§ 4. Condensation of Gases 165 

§ 5. Power of Removing Solid Matters from Solution 171 

§ 6. Permeability to Liquid Water. Imbibition. Capillary Power 176 

§ 7. Changes of Bulk by Drying and Frost 183 

§ 8. Adhesiveness 184 

§ 9. Relations to Heat 186 

CHAPTER V. 

The Soil as a Source of Food to Crops : Ingredients whose Elements 
ARE OP Atmospheric Origin. 

§ 1. The Free Water of the Soil in its Relations to Vegetable Nutrition 199 

§ 2. The Air of the Soil 217 

§ 3. Non-nitrogenous Organic Matters. Humus 222 

§ 4. The Ammonia of the Soil 238 

§ 5. Nitric Acid (Nitrates) of the Soil 251 

§ 0. Nitrogenous Organic Matters of the Soil. Available Nitrogen 274 

§ 7. Decay of Organic Matters 289 

§ 8. Nitrogenous Principles of Urine 293 

§ 9. Comparative Nutritive Value of Ammonia-Salts and Nitrates 300 



CONTENTS. IX 

CHAPTER VI. 

The Soil as a Source of Food to Crops : Ingredients whose Elements 
ARE Derived from Eocks. 

§ 1. General View of the Constitution of the Soil as Related to Vegetable 

Nutrition 305 

§ 2. Aqueous Solution of the Soil 309 

§ 3. Solution of the Soil in Strong Acids 329 

§ 4. Portion of Soil Insoluble in Acids 330 

§ 5. Reactions by which the Solubility of the Elements of the Soil Is al- 
tered. Solvent Effects of Various Substances. Absorptive and 

Fixing Power of Soils 331 

§ 6. Review and Conclusion 361 



INDEX. 



Absorption and displacement, law 

of 336 

Absorptive power of soils 333 

" " " cause of.343, 354 

" " " significance 

of 374 

Acids in soil 223 

" absorbed by soils 355 

Adhesion 165 

Adhesiveness of soils 184 

Air, atmospheric, composition of. . 21 
" within the plant, composition 

of 45 

Alkali-salts, solvent effect of 130 

Allotropism 66 

Alluvium 145 

Aluminum, alumina 107 

Amides 276 

Amide-like bodies 277, 300 

Ammonia ; 49, 54 

" absorbed by clay. . . .243, 267 

" » " peat 360 

" " " plants.... 56, 98 

" condensed in soils 240 

• " conversion of into nitric 

acid 85 

" evolved from flesh decay- 
ing under charcoal 169 

" fixed by gypsum 244 

" in atmosphere 54 

" " " how formed.77, 85 

" of rain, etc 60 

" of the soil, formation of. 239 
" " " chemically 

combined.243 
" " " physically 

condensed.240 

" quantity of.. 248 

" " " solubility of. 246 

" volatility of.. 244 

11 



Ammonia-salts and nitrates, nutri- 
tive value of 300 

Amphibole 112 

Analysis of soils, chemical indica- 
tions of 368 

" mechanical 147 

Apatite 116 

Apocrenates 231 

Apocrenic acid 227, 229 

Argillite 119 

Ash-ingredients, quantity needful 

for crops 363 

Atmosphere, chemical composi- 
tion 21, 22 

" physical constitution.. 99 

Atmospheric food, absorbed 99 

" " assimilated — 97 

Barley crop, ash ingredients of. — 364 

Basalt 120 

Bases, absorbed by soils 335, 359 

Bisulphide of iron 115 

Burning of clay 185 

Calcite 115 

Capillarity 175, 199, 201 

Carbohydrates in soil 222 

Carbon, fixed by plants 43, 48 

" in decay 291 

" supply of 95 

Carbonate of lime 115, 162 

" "magnesia 115,162 

Carbonic acid 38 

" " absorbed by soil 221 

" " " " plants.41, 

45, 98 
" exhaled by plants.. 43, 99 

" in the soil 218 

" " " water of soil.. 220 

" " quantity in the air.40, 

47, 94 
" " solubility in water .40, 130 



XII 



HOW CROPS FEED. 



Carbonic acid, solvent action of 128 

Carbonic oxide 92 

Chabasite 115 

" action on saline com- 
pounds 345 

" formed in Roman mason- 
ry 351 

Challs soils 192 

Charcoal, absorbs gases 165 

^ " defecating action of. 174 

Chili saltpeter 253 

Chlorite 113 

Chrysolite 114 

Clay 132, 134, 154 

" absorptive power 174 

" effect of, on urine 293 

Clay-Blate 119 

Coffee, condenses gases 168 

Color of soil 190 

Conglomerates 121 

Crenates 231 

Crenic acid 227, 229 

Decay 289 

Deliquescence 163 

Deserts 197 

Dew 189, 195 

Diffusion of gases 100 

Diorite 120 

Dolerite 120 

Dolomite 115, 121 

Draining 185 

Drain water, composition of 312 

Drift 144 

Dye stuffs, fixing of 174 

Earth-closet 171 

Eremacausis 289 

Evaporation, produces cold 188 

" amount of, from soil. 197 

Exhalation 202, 206 

Exposure of soil 195 

Feldspar 108 

" growth of barley in 100 

Fermentation 290 

Fixtation of bases in the soil 339 

Frost, effects of, on rocks 124 

" " " on soils 184,185 

Fumicacid 258 

Gases, absorbed by the plant 103 

" " " porous bodies.. 167 

" soils 165,166 

" diffusion of 100 

" osmose of 102 

Glaciers 124 



Glycine 296 

Glycocoll 296 

Gneiss... 119 

Granite 118, 120 

Gravel 152 

" warmth of 195 

Guanin 296 

Gypsum 115 

" does not directly absorb 

water 162 

" fixes ammonia 244 

Hardpan 156 

Heat, absorption and radiation of. . 

188, 193 

" developed in flowering 24 

" of soil 187 

Hippuric acid 295, 277 

Hornblende 112 

Hydration of minerals 127 

Hydraulic cement 122 

Hydrochloric acid gas 93 

Hydrogen, supply of, to plants 95 

" In decay 291 

Hydrous silicates, formation of 352 

Hygroscopic quality. 164 

Humates 230 

Humic acid. 226, 229 

Humin 236, 229 

Humus 136, 224, 276 

" absorbent power for water. . 162 
" absorbs salts from solutions. 172 

" action on minerals 138 

" chemical nature of 138 

" does it feed the plant ? 232 

" not essential to crops 238 

" value of 182 

Iodine in sea-water 322 

Isomorphism Ill 

Kreatin 19(5 

Kaolinite 113, 132 

Latent heat 188 

Lawes' and Gilbert's wheat experi- 
ments 372 

Leucite 113 

Lime, effects of 184, 185 

Limestone 121, 122 

Loam 154 

Lysimeter 314 

Magnesite 115 

Marble 121 

Marl 155 

Marsh gas 91, 99 

Mica 109 



INDEX. 



XIII 



Mica slate 119 

Minerals 106, 108 

" hydration of. 127 

" Bolution of 12T 

" variable composition of. . ..110 
Moisture, effect of, on temperature 

of soil 195 

Mold 156 

Moor-bed pan — 157 

Muck 155 

Nitrate of ammonia 71, 73 

" " " in atmospliere. 89 

Nitrates 252 

" as food for plants 271 

" formed in soil 171, 179 

" in water 270 

" loss of. 270 

" reduction of 73,82, 85 

" " "in soil 268 

" tests for 75 

Nitric acid 70 

" " as plant-food 90,98 

" " deportment towards the 

soil 357 

" " in atmosphere 86 

" " " rain-water 86 

" " " soil 251, 254 

" " " " sources of 256 

Nitric oxide 72 

Nitric peroxide 73 

Nitrification 252, 286 

" conditions of 265, 292 

Nitrogen, atmospheric supply to 

plants 95 

" combined, in decay. 291, 292 

" of the soil... 275 

" combined, of the soil, 

available 283 

" combined, of the soil, 

inert 278 

" combined, of the soil, 

quantity needed for crops.2SS 
" free, absorbed by soil. . .167 

'■'• " assimilated by the 

soil 259 

" " in soil 218 

" " not absorbed by 

vegetation 26, 99 

" " not emitted by liv- 
ing plants 23 

Nitrogen-compounds, formation of, 

in atmosphere. 75, 77, S3 



Nitrogenous fertilizers, effect on 

cereals ... 83 
Nitrogenous organic matters of soil. 274 

Nitrous acid 72 

Nitrous oxide 71, 93 

Ocher 156 

Oxidation, aided by porous bodies. 

169, 170 

Oxide of iron, a carrier of oxygen. .257 

" " hydrated,in the soil.350 

Oxygen, absorbed by plants 98 

" essential to growth 23 

" exhaled by foliage 25, 99 

" function of, in growth 24 

" in soil 218 

" supply 94 

" weathering action of 131 

Ozone 63 

" concerned in oxidation of ni- 
trogen 82 

" formed by chemical action. 66, 67 
" produced by vegetation. 67, 84, 99 
" relations of, to vegetable nu- 
trition 70 

Pan, composition of 352 

Parasitic plants, nourishment of. . .235 

Peat 155,224 

" nitrogen of 274 

Phosphate of lime 116 

Phosphoric acid fixed by the soil . . .357 
" " presence in soil 

water 315 

Phosphorite 116 

Plant-food, concentration of. 320 

" maintenance of supply. 371 

Platinized charcoal .170 

Platinum sponge, condenses oxygenl70 

Porphyry 120 

Potash, quantity in barley crop 363 

Provence, drouths of 198 

Pyrites 115 

Pyroxene 112 

Pumice 120 

Putrefaction 290 

Quartz 108, 122 

Eain-water, ammonia in 60, 88 

" nitric acid in 86 

" phosphoric acid in 94 

Ree Ree bottom, soil of 160 

Respiration of the plant 43 

Rocks 106, 117 

" attacked by plants 140 



x.\v 



HOW CROPS FEED. 



Rocks, conversion into soils 122 

Roots, direct action on soil 32fi 

Saline incrustations 179 

Saltpeter 252 

Salts decomposed or absorbed by 

the soil 336 

Sand 153,162 

Sand filter 172 

Sandstone 121 

Serpentine 114, 121 

Schist, micaceous 119 

" talcosc 121 

'* chlorite 121 

Shales 122 

Sherry wine region 192 

Shrinking of soils 183 

Silica 108 

" function in the soil 353 

" of soil, liberated by strong 

acids 330 

Silicates 109 

" zeolitic, presence in soils. .349 

Silicic acid, fixed in the soil 358 

Silk, hygroscopic 165 

Soapstone 121 

Sod, temperature of 199 

Soil 104 

" absorptive power of 333 

" aid to oxidation 170 

" aqueous solution of. . . .309, 323, 328 

" condenses gases 165, 166 

" capacity for heat 194 

" chemical action in 331 

" composition of. 362, 369 

" exhaustion of. 373 

" inei't basis. 305 

" natural strength of. . ., .372 

" origin and formation.. 106, 122, 135 

" physical characters 157 

" porosity of. 176 

" portion insoluble in acids 330 

" relative value of ingredients 367 

" reversion to rock 332 

" solubility in acids 329 

" " water 309 

" source of food to crops 305 

" state of division 159 

Soils, sedentary 143 

" transported 143 

" weight of 158 

Solubility, standards of 308 



Solution of soil in acids 370 

" " " water 310 

Steatite 121 

Swamp muck 155 

Sulphates, agents of oxidation 258 

Sulphate of lime 115 

Sulphur, in decay 293 

Sulphurous acid 94 

Sulphydric acid 94 

Syenite 120 

Talc 113 

Temperature of soil 186, 187, 194 

Transpiration 202, 208 

Trap rock 120 

TJlmates 230 

Ulmic acid 224, 226, 229 

Ulmin 224, 226, 229 

Urea 294,277 

Uric acid 295, 277 

Urine 293 

" preserved fresh by clay 293 

" its nitrogenous principles as- 
similated by plants 296 

Vegetation, antiquity of 138 

" decay of. 137 

" action on soil 140 

Volcanic rocks, conversion to soil.. 135 

Wall fruits 199 

Water absorbed by roots 202, 210 

" functions of, in nutrition of 

plant 216 

" imbibed by soil 180 

" movements in soil 177 

" proportion of in plant, influ- 
enced by soil 213 

" of soil 315,317 

" " bottom water 200 

" capillary... 200 

" hydrostatic 199 

" hygroscopic 201 

" quantity favorable to crops, .214 

Water-currents 124 

Water-vapor, absorbed by soil. 161, 164 

" exhaled by plants 99 

" not absorbed by 

plants 35, 99 

" of the atmosphere 34 

Weathering 131-134 

Wilting 203 

Wool, hygroscopic 164 

Zeolites 114,349 



HOW CROPS FEED 



H0¥ CROPS EEED. 



INTRODUCTION. 



In his treatise entitled " How Crops Grow," the author 
has described in detail the Chemical Composition of Agri- 
cultural Plants, and has stated what substances are indis- 
pensable to their growth. In the same book is given an 
account of the apparatus and processes by which the plant 
takes up its food. The sources of the food of crops are, 
however, noticed there in but the briefest manner. The 
present work is exclusively occupied with the important 
and extended subject of Vegetable Nutrition, and is thus 
the complement of the first-mentioned treatise. Whatever 
information may be needed as preliminary to an under- 
standing of this book, the reader may find in " How Crops 
Grow." * 

That crops grow by gathering and assimilating food is 
a conception with which all are familiar, but it is only by 
following the subject into its details that we can gain hints 
that shall apply usefully in Agricultural Practice. 



* It has been at least the anthor's aim to make the first of this series of books 
prepare the way for the second, as both the first and the second are written to 
malve possible an intelligible acconnt of the mode of action of Tillage and of 
Fertilizers, which will be the subject of a third work. 

17 



18 HOW CROPS FEED. 

When a seed germinates in a medium that is totally- 
destitute of one or all the essential elements of the plant, 
the embryo attains a certain development from the mate- 
rials of the, seed itself (cotyledons or endosperm,) but 
shortly after these are consumed, the plantlet ceases to in- 
crease in dry weight,* and dies, or only grows at its own 
expense. 

A similar seed deposited in ordinary soil, watered with 
rain or spring water and freely exposed to the atmosphere, 
evolves a seedling which survives the exhaustion of the 
cotyledons, and continues without cessation to grow, 
forming cellulose, oil, starch, and albumin, increases many 
times — a hundred or two hundred fold — in weight, runs 
normally through all the stages of vegetation, blossoms, 
and yields a dozen or a hundred new seeds, each as perfect 
as the original. 

It is thus obvious that Air, Water, and Soil, are capa- 
ble of feeding plants, and, under purely natural conditions, 
do exclusively nourish all vegetation. 

In the soil, atmosphere, and water, can be found no 
trace of the peculiar organic principles of plants. We 
look there in vain for cellulose, starch, dextrin, oil, or al- 
bumin. The natural sources of the food of crops consist 
of various salts and gases which contain the ultimate ele- 
ments of vegetation, but which require to be collected and 
worked over by the plant. 

The embryo of the germinating seed, like the bud of a 
tree when aroused by the spring warmth from a dormant 
state, or like the sprout of a potato tuber, enlarges at the 
expense of previously organized matters, supplied to it 
by the contiguous parts. 

As soon as the plantlet is weaned from the stores of the 



* Since vegetable matter may contain a variable amount of water, either that 
which belongs to the sap of the fresh plant, or that which is hygroscopically re- 
tained in the pores, all comparisons must be made on the dry, i. e., water-free 
substance. See "How Crops Grow," pp. 53-5. 



INTEODUCTION. 19 

mother seed, the materials, as well as the mode of its nu- 
trition, are for the most part completely changed. Hence- 
forth the tissues of the plant and the cell-contents must 
be principally, and may be entirely, built up from purely 
inorganic or mineral matters. 

In studying the nutrition of the plant in those stages 
of its growth that are subsequent to the exhaustion of the 
cotyledons, it is needful to investigate separately the nu- 
tritive functions of the Atmosphere and of the Soil, for 
the important reason that the atmosphere is nearly con- 
stant in its composition, and is beyond the reach of human 
influence, while the soil is infinitely variable and may be 
exhausted to the verge of unproductiveness or raised to 
the extreme of fertility by the arts of the cultivator. 

In regard to the Atmosphere, we have to notice minutely 
the influence of each of its ingredients, including Water 
in the gaseous form, upon vegetable production. 

The evidence has been given in " How Crops Grow," which 
establishes what fixed earthy and saline matters are essential 
ingredients of plants. The Soil is plainly the exclusive 
source of all those elements of vegetation which cannot as- 
sume the gaseous condition, and which therefore cannot ex- 
ist in the atmosphere. The study of the soil involves a con- 
sideration of its origin and of its manner of forniation. The 
productive soil commonly contains atmospheric elements, 
which are important to its fertility ; the mode and extent 
of their incorporation with it are topics of extreme prac- 
tical importance. We have then to examine the signif- 
icance of its water, of its ammonia, and especially of its 
nitrates. These subjects have been recently submitted to 
extended investigations, and our treatise contains a large 
amount of information pertaining to them, which has never 
before appeared in any publication in the English tongue. 
Those characters of the soil that indirectly affect the 
growth of plants are of the utmost moment to the farm- 
er. It is through the soil that a supply of solar heat, with- 



20 HOW CROPS FEED. 

out which no life is possible, is largely influenced. Water, 
whose excess or deficiency is as j^ernicious as its proper 
quantity is beneficial to crops, enters the plant almost 
exclusively through its roots, and hence those qualities 
of the soil which are most favorable to a due supply of 
this liquid demand careful attention. The absorbent pow- 
er of soils for the elements of fertilizers is a subject which 
is treated of with considerable fullness, as it deserves. 

Our book naturally falls into two divisions, the first of 
which is devoted to a discussion of the Relations of the 
Atmosphere to Vegetation, the second being a treatise on 
the Soil 



DIVISION I. 

THE ATMOSPHERE AS RELATED TO 
VEGETATION. 

CHAPTER I. 

ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 

§ 1. 
CHEMICAL COMPOSITION OF THE ATMOSPHERE. 

A multitude of observations has demonstrated that 
from ninety-five to ninety-nine per cent of the entire mass 
(weight) of agricultural plants is derived directly or indi- 
rectly from the atmosphere. 

The general composition of the Atmosphere is familiar 
to all. It is chiefly made up of the two elementary gases, 
Oxygen and Nitrogen, which have been described in " How 
Crops Grow," pp. 33-39.* These two bodies are present 
in the atmosphere in very nearly, though not altogether, 
invariable proportions. Disregarding its other ingredients, 
the atmosphere contains in 100 parts 

By weight. By volume. 

Oxygen 23.17 30.95 

Nitrogen 76.83 79.05 

100.00 100.00 

Besides the above elements, several other substances oc- 



* In our frequent references to this boolc we shall employ the abbreviation 
H. C. G. 

21 



22 HOW CROPS FEED. 

cur or may occur in the air in minute and variable quanti- 
ties, viz. : 

Water, as vapor. . .average proportion by weight, i |ioo 

Carbonic acid gas " " " '* *|io-ooo 

Ammonia " " " " Mso-ooo-ooo? 

Ozone " " " " miuute traces. 

Nitric acid " " " " 

Nitrous acid " " " " 

Marsh gas " " " " 

Inairof(C^'"^«^^^«^^<le' " " " " 

•< Sulphurous acid, " " " " 

towns. ( siiipiiydric acid " " 

Miller gives for the air of England the following aver- 
age proportions by volume of the four most abundant in- 
gredients. — {Elements of Chemistry^ part II., p. 30, 3d Ed.) 

Oxygen 20.61 

Nitrogen 77.95 

Carbonic acid 04 

Water-vapor 1,40 



100.00 
We may now appropriately proceed to notice in order 
each of the ingredients of the atmosphere in reference to 
the question of vegetable nutrition. This is a subject re- 
garding which unaided observation can teach us little or 
nothing. The atmosphere is so intangible to the senses 
that, without some finer instruments of investigation, we 
should forever be in ignorance, even of the separate exist- 
ence of its two principal elements. Chemistry has, how- 
ever, set forth in a clear light many remarkable relations 
of the Atmosphere to the Plant, whose study forms one 
of the most instructive chapters of science. 



RELATIONS OF OXYGEN GAS TO VEGETABLE NUTRITION. 

Absorption of Oxygen Essential to Growtli.— The ele- 
ment Oxygen is endowed with great chemical activity. 
This activity we find exhibited in the first act of vegeta- 



ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 



23 



tioD, viz.: in germination. We know that the presence of 
oxygen is an indispensable requisite to the sprouting seed, 
and is possibly the means of provoking to action the dor- 
mant Hfe of the germ. The ingenious experiments of Traube 
(H. C. G., p. 326.) demonstrate conclusively that free 
oxygen is an essential condition of the growth of the 
seedling plant, and must have access to the plumule, and 
especially to the parts that are in the act of elongation. 

T>e Saussure long ago showed that oxygen is needful to 
the development of the buds of maturer plants. He ex- 
perimented in the following manner : Several woody twigs 
(of willow, oak, apple, etc.) cut 
in spring-time just before the 
buds should unfold were placed 
under a bell-glass containing 
common air, as in fig. 1. Their 
cut extremities stood in water 
held in a small vessel, while the 
air of the bell was separated 
from the external atmosphere by 
the mercury contained in the 
large basin. Thus situated, the 
buds opened as in the free air, 
and oxygen gas was found to be 
consumed in considerable quan- 
tity. When, however, the twigs were confined in an 
atmosphere of nitrogen or hydrogen, they decayed, with- 
out giving any signs of vegetation. {Becherches sur la 
Vegetation^ p. 115.) 

The same acute investigator found that oxygen is ab- 
sorbed by the roots of plants. Fig. 2 shows the arrange- 
ment by which he examined the effect of different gases 
on these organs. A young horse-chestnut plant, carefully 
lifted from the soil so as not to injure its roots, had the' 
latter passed through the neck of a bell-glass, and the stem 
was then cemented air-tight into the opening. The bell 




Fig. 1. 



24 



HOW CliOPS FEED. 



was placed in a "basin of mercury, C, D, to shut off its con- 
tents from the external air. So much water was intro- 
duced as to reach the ends of the principal roots, and the 
space above was occupied by com- 
mon or some other kind of air. In 
one experiment carbonic acid, in a 
second nitrogen, in a third hydro- 
gen, and in three others common 
air, was employed. In the first the 
roots died in seven or eight days, 
in the second an4 third they perish- 
ed in thirteen or fourteen days, 
while in the three others they re- 
mained healthy to the end of three 
weeks, when the experiments were 
concluded. {Recherches, p. 104.) 
Flowers require oxygen for their 
development. Aquatic plants send 
their flower-buds above the water 
to blossom. De Saussure found 
that flowers consume, in 24 hours, 
several or many times their bulk of oxygen gas. This 
absorption proceeds most energetically in the pistils and 
stamens. Flowers of very rapid growth experience in 
this process, a considerable rise of temperature. Garreau, 
observing the spadix of Arum itaUcum, which absorbed 
28|- times its bulk of oxygen in one hour, found it 15° F. 
warmer than the surrounding air. In the ripening of 
fruits, oxygen is also absorbed in small quantity. 

The Function of Free Oxygen. — All those processes 
of growth to which free oxygen gas is a requisite appear 
to depend upon the transfer to the growing organ of mat- 
ters previously organized in some other part of the plant, 
and probably are not cases in which external inorganic 
bodies are built up into ingredients of the vegetable struc- 
ture. Young seedlings, buds, flowers, and ripening fruits, 




Tig. 3. 



ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 25 

have no power to increase in mass at the expense of the 
atmosphere and soil; they have no provision for the ab- 
sorption of the nutritive elements that surround them ex- 
ternally, but grow at the expense of other parts of the plant 
(or seed) to which they belong. The function of free 
gaseous oxygen in vegetable nutrition, so far as can be 
judged from our existing knowledge, consists in effecting 
or aiding to effect the conversion of the materials which 
the leaves organize or which the roots absorb, into the 
proper tissues of the growing parts. Free oxygen is thus 
probably an agent of assimilation. Certain it is that the 
free oxygen which is absorbed by the plant, or, at least, a 
corresponding quantity, is evolved again, either in the un- 
combined state or in union with carbon as carbonic acid. 
Exhalation of Oxygen from Foliage. — The relation of 
the leaves and green parts of plants to oxygen gas has 
thus far been purposely left unnoticed. These organs like- 
wise absorb oxygen, and require its presence in the atmos- 
phere, or, if aquatic, in the water which surrounds them ; 
but they also, during their exposure to light^ exhale oxygen. 
This interesting fact is illustrated j^ppE^|^ 

by a simple experiment. Fill a |llifez^f;r^'"'^^ 
glass funnel with any kind of fresh I^^^Bln^H/ 

leaves, and place it, inverted, in a '^^IHIi^^l 

wide glass containing water, fig. ^lifflwi^W 

3, so that it shall be completely ^^j^BlHj&ligB^Ml 
immersed, and displace all air from j^^^Jl^WI^^^B 
its interior by agitation. Close the r^ ^ z^^"'^ "^ 3?^^B 
neck of the funnel air-tight by iiiiillililll llillillilllillllllllli 
a cork, and pour off a portion ^^S- 3. 

of the water from the outer vessel. Expose now the 
leaves to strong sunlight. Observe that very soon minute 
bubbles of air will crather on the leaves. These will 
gradually increase in size and detach themselves, and 
after an hour or two, enough gas will accumulate in 
the neck of the funnel to enable the experimenter to 
2 



26 HOW CROPS FEED. 

prove that it consists of oxygen. For this purpose bring 
the water outside the neck to a level with that inside; 
have ready a splinter of pine, the end of which is glow- 
ing hot, but not in flame, remove the cork, and insert the 
ignited stick into the gas. It will inflame and burn much 
more brightly than in the external air. (See H. C. G., p. 
35, Exp. 5.) To this phenomenon, one of the most im- 
portant connected with our subject, we shall recur under 
the head of carbonic acid, the compound which is the 
chief source of this exhaled oxygen. 



§ 3. 
RELATIONS OF NITROGEN GAS TO VEGETABLE NUTRITION. 

IVitrogen Gas not a Food to the Plant.— Nitrogen in 
the free state appears to be indifferent to vegetation. 
Priestley, to whom we are much indebted for our knowl- 
edge of the atmosphere, was led to believe in 1779 that 
free nitrogen is absorbed by and feeds the plant. But 
this philosopher had no adequate means of investigating 
the subject. De Saussure, twenty years later, having 
command of better methods of analyzing gaseous mix- 
tures, concluded from his experiments that free nitrogen 
does not at all participate in vegetable nutrition. 

Boussingault's Experiments. — The question rested un- 
til 1837, when Boussingault made some trials, which, how- 
ever, were not decisive. In 1851-1855 this ingenious 
chemist resumed the study of the subject and conducted 
a large number of experiments with the greatest care, 
all of which lead to the conclusion that no appreciable 
amount of free nitrogen is assimilated by plants. 

His plan of experiment was simj)ly to cause plants to 
grow in circumstances where, every other condition of de- 
velopment being supplied, the only source of nitrogen at 



ATMOSPHEEIC AIE AS THE FOOD OF PLANTS. 



27 



their command, besides that contained in the seed itself, 
should be the free nitrogen of the atmosphere. For tliis 
purpose he prepared a soil consisting of pumice-stone and 
the ashes of stable-manure, which was perfectly freed from 
all compounds of nitrogen by treatment w^ith acids and in- 
tense heat. In nine of his earlier experiments the soil thus 
prepared was placed at the bottom of a large glass globe, 
B, fig. 4, of 15 to 20 gallons' capacity. Seeds of cress, 
dwarf beans, or lupins, were deposited in the soil, and a 
proper supply of water, purified for the purpose, was add- 
ed. After germination of the seeds, a glass globe, i>, of 
about one-tenth the capacity of the larger vessel, was filled 
with carbonic acid (to supply carbon), and was secured air- 
tight to the mouth 
of the latter, com- 
munication being 
bad between them 
by the open neck at 
C. The apparatus 
was then disposed in 
a suitably lighted 
place in a garden, 
and left to itself for 
a period which va- 
ried in the difierent 
experiments from 14- 
to 5 months. At 
the conclusion of the 
trial the plants were 
lifted out, and, to- 
gether with the soil 
from which their roots could not be entirely separated, 
were subjected to chemical analysis, to determine the 
amount of nitrogen which they had assimilated during 
growth. 

The details of these trials are contained in the subjoined 




Fiff. 4. 



28 



HOW CEOPS FEED. 



Table. The weights are expressed in the gram and its 
fractions. 



Kind of Plant. 



Duration 

of 

Expenment. 









ii 



^^ 









Dwarf bean. 

Oat 

Bean 



2 months 

2 

3 



Oat . . . 
Lupin. 



Dwarf bean. 

Cress 

Lupin 



21/2 " 

2 

7 weeks 



2 months 

as manure 
5 months 
as manure 



0.780 

0.377 

0.530 

0.618 

0.139 

0.825 

2.202 

0.600 

0.343 

0.686 

0.792 

0.665 

0.008 ( 

0.0261" 

0.627 \ 

2.512 f 



1.87 
0.54 
0.89 
1.13 
0.44 
1.82 
6.73 
1.95 
1.05 
1.53 

2.;^ 

2.80 
0.65 

5.76 



0.0349 0, 
0.0078 0. 
0.02100, 
0.0245|0. 
0.00310. 



0.0480 
0.1282 
0.0349 
0.0200 
0.0399 
0.0354 
0.0298 

0.0013 
0.1827 



Sum 11. '720 30.11 0.6135 0.5868—0.0247 



0340 
0067 
0189 
0226 
0030 
0483 
1246 
0339 
0204 
0397 
0360 
0277 

0013 



0.1697 



—0.0009 
-0.0011 
—0.0021 
—0.0019 
—0.0001 
+0.0003 
—0.0036 
—0.0010 
+0.0004 
—0.0002 
+0.0006 
—0.0021 

0.0000 
—0.0130 



While it must be admitted that the unavoidable errors of 
experiment are relatively large in working with such small 
quantities of material as Boussingault here employed, we 
cannot deny that the aggregate result of these trials is de- 
cisive against the assimilation of free nitrogen, since there 
was a loss of nitrogen in the 14 experiments, amounting 
to 4 per cent of the total contained in the seeds ; while a 
gain was indicated in but 3 trials, and was but 0.13 per 
cent of the nitrogen concerned in them. — (Boussingault's 
Agro)iomie, Chimie Agricole, et Physiologie^ Tome I, 
pp. 1-64.) 

The Opposite Conclusions of Ville.— In the years 1849, 
'50, '51, and '52, Georges Ville, at Grenelle, near Paris, 
experimented upon the question of the assimilability of free 
nitrogen. His method was similar to that first employed 
by Boussingault. The plants subjected to his trials were 
cress, lupins, colza, wheat, rye, maize, sun-flowers, and to- 
bacco. They were situated in a large octagonal cage 
made of iron sashes, set with glass-plates. The air was 



ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 



29 



constantly renewed, and carbonic acid was introduced in 
proper quantity. The experiments w^ere conducted on a 
larger scale than those of Boussingault, and their result 
was uniformly the reverse. Yille indeed thought to have 
established that vegetation feeds on the free nitrogen of 
the air. To the conclusions to which Boussingault drew 
from the trials made in the manner already described, Yille 
objected that the limited amount of air contained in the 
glass globes was insufficient for the needs of vegetation ; 
that plants, in fact, could not attain a normal development 
under the conditions of Boussingault's experiments. — 
(Ville, Mecherches sur la Vegetation^ pp. 29-58, and 53-98.) 

Boussingault's Later Experiments.— The latter there- 
upon instituted a new series of trials in 1854, in which 
he proved that the plants he had previously experimented 
upon attain their full development in a confined atmosphere 
under the circumstances of his first experiments, provided 
they are supplied with some assimilable compound of 7ii- 
trogen. He also conducted seven new experiments in an 
apparatus which allowed the air to be constantly renewed, 
and in every instance confirmed his former results. — 
{Agro7iomie, Chimie Agricole et Physiologie^ Tome I, 
pp. 65-114.) 

The details of these experiments are given in the follow- 
ing Table. The w^eights are expressed in grams. 



j 


Kind of Plant. 


Duratim 

of 

Experiment. 




jl 


it 


•a 


^ 
f 




1 

9, 


Lupin 

Bean 


10 weeks 
10 " 

12 " 
14 " 

13 " 
( 9 - 

1 as manure 
j 10 weeks 
(as manure 


1 
1 
1 
1 

2 
1 
1 

30 
12 


0.337 
0.720 
0.748 
0.755 
1.510 


2.140 
2.000 
2.847 
2.240 
5.150 


0.0196 0.0187 
0.0322 0.0325 
0.03350.0341 
0.0339 0.0329 
0.0676,0.0666 

0.0355^0.0324 
0.00460.0052 


-0.0009 
+0.0003 
+0.0006 


8 


Bean 


4 




-O.OOIO 


5 


Bean 


—0.0010 


6 


Lupin 


Ofin 1.730 


—0.0021 


7 


Cress 


0.300 f 
■ 0.100 


0.533 


+0.0006 












Sum 


.4.780 


16.64 


2269 


0.2.^0 


-0.0035 



30 HOW CROPS FEED. 

Inaccuracy of Ville's Results. — In comparing the in- 
vestigations of Boussingault and Ville as detailed in their 
own words, the critical reader cannot fail to be struck 
with the greater simplicity of the apparatus used by the 
former, and his more exhaustive study of the possible 
sources of error incidental to the investigation — facts which 
are greatly in favor of the conclusions of this skillful and 
experienced philosoi^her. Furthermore Cloez, who was 
employed by a Commission of the French Academy to 
oversee the repetition of Ville's experiments, found that a 
considerable quantity of ammonia was either generated 
within or introduced into the apparatus of Ville during 
the period of the trials, which of course vitiated all his 
results. 

Any further doubts with regard to this important sub- 
ject have been effectually disposed of by another most 
elaborate investigation. 

Research of Lawes, Gilbert, and Pugh,— In 1857 and 
'58, the late Dr. Pugh, afterward President of the Penn- 
sylvania Agricultural College, associated himself with 
Messrs. Lawes and Gilbert, of Rothamstead, England, 
for the purpose of investigating all those points con- 
nected with the subject, which the spirited discussion of 
the researches of Boussingault and Ville had suggested as 
possibly accounting for the diversity of their results. 
Lawes, Gilbert, and Pugh, conducted 27 experiments on 
graminaceous and leguminous plants, and on buckwheat. 
The plants vegetated wathin large glass bells. They were 
cut off from the external air by the bells dipping into 
mercury. They were supplied with renewed portions of 
purified air mixed with carbonic acid, which, being forced 
into the bells instead of being drawn through them, ef- 
fectually prevented any ordinary air from getting access 
to the plants. 

To give an idea of tlie mode in wliicli these delicate investigations are 
conducted, we give here a figure and concise description of the appara- 



ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 31 




Fig. 5. 



32 HOW CROPS FEED. 

tus employed by Lawes, Gilbert, and Pugh, in their experiments made in 
the year 1858. 

A, fig. 5, represents a stone-ware bottle 18 inches in diameter and 24 
inches high. 

£, C, and E, are glass 3-necked bottles of about 1 quart capacity. 

i<' is a large glass shade 9 inches in diameter and 40 inches high. 

a represents the cross-section of a leaden pipe, which, passing over all 
the vessels A of the series of 16, supplied them with water, from a reser- 
voir not shown, through the tube with stop-cock a b. 

c d eis a. leaden exit-tube for air. At c it widens, until it enters the 
vessel^., and another bent tube, q r s, passes through it and reaches to 
the bottom of J., as indicated by the dotted lines. The latter opens at 
q, and serves as a safety tube to prevent water passing into d e. 

The bottles B C are partly filled with strong sulj)huric acid. 

The tube Z> 2>, 1 inch wide and 3 feet long, is filled with fragments of 
pumice-stone saturated with sulphuric acid. At// indentations are made 
to prevent the acid from draining against the corks with which the tube 
is stopped. 

The bottle E contains a saturated solution of pure carbonate of soda. 

^ 7i is a bent and caoutchouc-jointed glass tube connecting the interior 
of the bottle E with that of the glass shade F. 

% ky better indicated in 2, is the exit-tube for air, connecting the 
interior of the shade F with an eight-bulbed apparatus, J/, containing 
sulphuric acid. 

wwis a, vessel of glazed stone-ware, containing mercury in a circular 
groove, into which the lower edge of the shade F is dipped. These 
glass tubes, g A, ti v, and i k, 2, pass under the edge of the shade and 
communicate with its interior, the mercury cutting off all access of ex- 
terior air, except through the tubes. Another tube, n o, passes air-tight 
through the bottom of the stone-ware vessel, and thus communicates 
with its interior. 

The tubes w v and i k are seen best in 2, which is taken at right 
angles to 1. 

The plants were sprouted and grew in pots, v, within the shades. The 
tube u V was to supply them with water. 

The water which exhaled from the foliage and gathered on the inside 
of the shade ran off through n o into the bottle 0. This water was re- 
turned to the pots through u v. 

The renewed supply of pure air was kept up through the bottles and 
tube J., B, C, D, E. On opening the cock a b, A, water enters A, and 
its pressure forces air through the bottles and tube into the shade F, 
whence it finds its exit through the tube i ^•, and the bulb-apparatus 3f. 
In its passage through the strong sulphuric acid of B, C, and D, the air 
is completely freed from ammonia, while the carbonate of soda of ^re- 
moves any traces of nitric acid. The sulphuric acid of the bulb M puri- 
fies the small amount of air that might sometimes enter the shade 
through the tube i k, owing to cooling of the air in F, when the current 



ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 33 

was not passing. The outer ends of the tubes t and i(, were closed wUh 
caoutchouc tubes and glass plugs. 

In these experiments it was considered advisable to furnish to the 
plants more carbonic acid than the air contains. This was accomplished 
by pouring liydrochlorie acid from time to time into the bottle T, which 
contained fragments of marble. The carbonic acid gas thus liberated 
joined, and was swept on by the current of air in C. Experiments taught 
how much hydrochloric acid to add and how often. The proportion of 
this gas was kept within the limits which previous experimenters had 
found permissible, and was not allowed to exceed 4.0 per cent, nor to 
fall below 0.2 per cent. 

In these experiments tlie seeds were deposited in a soil purified from 
nitrogen-compounds, by calcination in a current of air and siibsequeut 
washing with pure water. To this soil was added about 0.5 per cent of 
the ash of the plant which was to grow in it. The water used for wa- 
tering the plants was specially purified from ammonia and nitric acid. 
The experiments of Lawes, Gilbert, and Pugh, fully 
confirmed those of Boussingault. For the numerous de- 
tails and the full discussion of collateral points bearing on 
the study of this question, we must refer to their elaborate 
memoir, " On the Sources of the Nitrogen of Vegetation," 
— (Philosophical Transactions, 1861, II, pp. 431-579.) 

Nitrogen Gas is not Elmitted. l>y l^iving I*la,mts.— It 
A^ras long supposed by vegetable physiologists that when the foliage of 
plants is exposed to the sun, free nitrogen is evolved by them in small 
quantity. In foct, when plants are placed in the circumstances which 
admit of collecting the gases that exhale from them under the action of 
light, it is found that besides ox3'gen a quantity of gas appears, which, 
unless special precautions are observed, consists chiefly of nitrogen, 
which was a part of the air that fills the intercellular spaces of the plant, 
or was dissolved in the water, in which, for the purposes of experiment, 
the plant is immersed. 

If, as Boussingault has recently (1863) done, this air be removed from 
the plant and water, or rather if its quantity be accurately determined 
and deducted from that obtained in the experiment, the result is that no 
nitrogen gas remains. A small quantity of gas besides oxygen was indeed 
usually evolved from the plant when submerged in water. The gas on 
examination proved to be marsh gas. 

Cloez was unable to find marsh gas in the air exhaled from either 
aquatic or land plants submerged in water, and in his most recent 
researches (1865) Boussingault found none in the gases given off from 
the foliage of a living tree examined without submergence. 

The ancient conclusion of Saussure, Dauben)^ Draper, and others, 
that nitrogen is emitted from the substance of the plant, is thus shown 
to have been based on an inaccurate method of investigation. 
2* 



34 HOW CKOPS FEED. 

§4. 

RELATIONS OF ATMOSPHERIC WATER TO VEGETABLE 
NUTRITION. 

Occurrence of Water in the Atmosphere.— If water be 

exposed to the air in a shallow, open vessel for some time, 
it is seen to decrease in quantity, and finally disappears en- 
tirely ; it evaporates, vaporizes, or volatilizes. It is con- 
verted into vapor. It assumes the form of air, and becomes 
a part of the atmosphere. 

The rapidity of evaporation is greater the more eleva- 
ted the temperature of the water, and the drier the atmos- 
phere that is over it. Even snow and ice slowly suffer 
loss of weight in a dry day though it be frosty. 

In this manner evaporation is almost constantly going 
on from the surface of the ocean and all other bodies of 
water, so that the air always carries a portion of aqueous 
vapor. 

On the other hand, a body or mixture whose tempera- 
ture is far lower than that of the atmosphere, condenses 
vapor from the air and makes it manifest in the form of 
water. Thus a glass of ice- water in a warm summer's day 
becomes externally bedewed with moisture. In a similar 
manner, dew deposits in clear and calm summer nights 
upon the surface of the ground, upon grass, and upon all 
exposed objects, whose temperature rapidly falls when 
they cease to be warmed by the sun. Again, when the 
invisible vapor which fills a hot tea-kettle or steam-boiler 
issues into cold air, a visible cloud is immediately formed, 
which consists of minute droplets of water. In like man- 
ner, fogs and the clouds of the sky are produced by the 
cooling of air charged with vapor. When the cooling is 
sufficiently great and sudden, the droplets acquire such 
size as to fall directly to the ground ; the water assumes 
the form of rain. 



ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 85 

"Water then exists in the atmosphere during the periods 
of vegetable activity as gas or vapor,* and as liquid. In 
the former state it is almost perpetually rising into the air, 
while in the latter form it frequently falls again to the 
ground. It is thus in a continual transition, back and 
forth, from the earth to the sky, and from the sky to the 
earth. 

We have given the average quantity of water-vapor in 
the air at one per cent ; but the amount is very variable, 
and is ahnost constantly fluctuating. It may range from 
less than one-half to two and a half or three per cent, ac- 
cording to temperature and other circumstances. 

When the air is damp, it is saturated with moisture, so 
that water is readily deposited upon cool objects. On the 
other hand, when dry, it is capable of taking up additional 
moisture, and thus facilitates evaporation. 

Is Atmospheric Water Absorbed by Plants 1— It has 

long been supposed that growing vegetation has the power 
to absorb vapor of water from the atmosphere by its 
foliage, as well as to imbibe the liquid water which in the 
form of rain and dew may come in contact with its leaves. 
Experiments which have been instituted for the purpose 
of ascertaining the exact state of this question have, how- 
ever, demonstrated that agricultural plants gather little or 
no water from these sources. 

The wilting of a plant results from the fact that the 
leaves suffer water to evaporate from them more rapidly 
than the roots can take it up. The speedy reviving of a 
wilted plant on the falling of a sudden rain or on the depo- 
sition of dew depends, not so much on the absorption by 
the foliage, of the water that gathers on it, as it does 



* While there is properly no essential difference between a gas and a vapor, 
the former term is commonly applied more especially to aeriform bodies which 
are not readily brought to the liquid state, and the latter to those which are easily 
condensed to liquids or solids. 



36 HOW CROPS FEED. 

on the suppression of evaporation, which is a consequence 
of the saturation of the surrounding air with water. 

linger, and more recently Duchartre, have found, 1st, 
that plants lose weight (from loss of water) in air that is 
as nearly as possible saturated with vapor, when their 
roots are not in contact with soil or liquid water. Du- 
chartre has shown, 2d, that plants do not gain, but some- 
times lose weight when their foliage only is exposed to 
dew or even to rain continued through eighteen hours, al- 
though they increase in weight strikingly (from absorption 
of water through their roots,) when the rain is allowed to 
fall upon the soil in which they are planted. 

Knop has shown, on the other hand, that leaves, either 
separate or attached to twigs, gain weight by continued 
immersion in water, and not only recover what they may 
have lost by exposure, but absorb more than they orig- 
inally contained. (Yersuchs-JStatlonen, YI, 252.) 

The water of dews and rains, it must be remembered, 
however, does not often thoroughly wet the absorbent sur- 
face of the leaves of most plants ; its contact being pre- 
vented, to a great degree, by the hairs or wax of the 
epidermis. 

Finally, 3d, Sachs has found that even the roots of 
plants appear incapable of taking up watery vapor. 

To convey an idea of the method employed in such 
investigations, we may quote Sachs' account of one 
of his experiments. (V. St., II, 7.) A young camellia, 
having several fresh leaves, was taken from the loose 
soil of the pot in which it had been growing ; from 
its long roots all particles of earth were carefully remov- 
ed, and its weight was ascertained. The bottom of a 
glass cylinder was covered with water to a little depth, 
and the roots of the camellia were introduced, but not in 
contact with the water. The stem was supported at its 



ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 37 

lower part in a hole in a glass cover,* that was cemented 
air-tight u23on the vessel. The stem itself was cemented 
by soft wax into the hole, so that the interior of the ves- 
sel was completely cut off from direct communication with 
the external atmosphere. The plant thus situated had its 
roots in an atmosphere as nearly as possible saturated with 
vapor of water, while its leaves were exposed to the ex- 
ternal air. After four days had expired, the entire appa- 
ratus, plant included, had lost 1.823 grm. Thereupon the 
plant was removed from the vessel and weighed by itself; 
it had lost 2.188 grm. The loss of the entire apparatus 
was due to vapor of water, which had escaped through 
the leaves. The difference between this loss and the loss 
which the plant had experienced could be attributed only 
to an exhalation of water through the roots, and amount- 
ed to (2.188 — 1.823=) 0.365 grm. 

This exhalation of water into the confined and moist at- 
mosphere of the glass vessel is explained, according to 
Sachs, by the fact that the chemical changes proceeding 
within the plant elevate its temperature above that of the 
surrounding atmosphere. 

Knop, in experiments on the transpiration of plants, 
{V, St., VI, 255,) obtained similar results. He found, 
however, that a moist piece of paper or wood also lost 
weight when kept for some time in a confined space over 
water. He therefore concludes that it is nearly impossible in 
the conditions of such experiments to maintain the air sat- 
urated with vapor, and that the loss of weight by the roots 
is due, not to the heat arising from internal chemical 
changes, but to simple evaporation from their surface. In 
one instance he found that a portulacca standing over 
night in a bell-glass with moistened sides, did not lose, but 
gained weight, some dew having gathered on its foliage. 



* The cover consisted of two semicircular pieces of ground glass, each of 
which had a small semicircular notch, so that the two could be brought together 
by their straight edges around the stem. 



38 HOW CROPS FEED. 

The result of these investigations is, that while, perhaps, 
wilted foliage in a heavy rain may take up a small quan- 
tity of water, and while foliage and roots may absorb 
some vapor, yet in general and for the most part the at- 
mospheric water is not directly taken up to any great ex- 
tent by plants, and does not therefore contribute immedi- 
ately to their nourishment. 

Atmospheric Water Enters Crops through the Soil. — 
It is only after the water of the atmosphere has become in- 
corporated with the soil, that it enters freely into agricul- 
tural plants. The relations of this substance to proper 
vegetable nutrition may then be most appropriately dis- 
cussed in detail when we come to consider the soil. (See 
p. 199.) 

It is probable that certain air-plants (epiphytes) native to the tropics, 
•which have no connection with the soil, and are not rooted in a medium 
capable of yielding water, condense vapor from the air in considerable 
quantity. So also it is proved that the mosses and lichens absorb water 
largely from moist air, and it is well known that they become dry and 
brittle in hot weather, recovering their freshness and flexibility when the 
air is damp. 

§5. 

RELATIONS OF CARBONIC ACID GAS TO VEGETABLE 
NUTRITION. 

Composition and Properties of Carbonic Acid. — 

When 12 grains of pure carbon are heated to redness 
in 32 grains of pure oxygen gas, the two bodies unite to- 
gether, themselves completely disappearing, and 44 grains 
of a gas are produced which has the same bulk as the 
oxygen bad at the beginning of the experiment. The new 
gas is nearly one-half heavier than oxygen, and differs in 
most of its properties from both of its ingredients. It is 
carbonic acid. This substance is the product of the burn- 
ing of charcoal in oxygen gas, (H. C. G., p. 35, Exp. 6.) 
It is, in fact, produced whenever any organic body is 



ATMOSPHERIC AIR AS THE POOD OF PLANTS. 39 

burned or decays in contact with the air. It is like oxy- 
gen, colorless, but it has a jDcculiar pungent odor and 
pleasant acid taste. 

The composition of carbonic acid is evident from what 
has been said as to its production from carbon and oxygen. 
It consists of two atoms, or 32 parts by weight, of oxygen, 
united to one atom, or 12 parts, of carbon. Its symbol is 
CO^. In the subjoined scheme are given its symbolic, 
atomic, and percentage composition. 





At wt. 


Jfe?* cefit. 


c 


= 13 


37.27 


Oo 


= 33 


73.73 



CO. = U 100.00 

In a state of combination carbonic acid exists in nature 
in immense quantities. Limestone, marble, and chalk, 
contain, when pure, 44 per cent of this acid united to lime. 
These minerals are in chemical language carbonate of lime. 
Common saloeratus is a carbonate of potash, and soda- 
salaeratus is a carbonate of soda. 

From either of these carbonates it is easy to separate 
this gas by the addition of another and stronger acid. 

For this purpose we may employ the Rochelle or Seidlitz powders so 
commonly used in medicine. If we mingle together in the dry state the 
contents of a blue paper, which contains carbonate of soda, with those of 
a white paper, which consist of tartaric acid, nothing is observed. If, 
however, the mixture be placed at the bottom of a tall bottle, and a little 
water be poured upon it, at once a vigorous bubbling sets in, which is 
caused by the liberated carbonic acid.* 

Some important properties of the gas thus set free may be readily 
made manifest by the following cxpei-imeuts. 

a. If a burning taper or match be immersed in the gas, the flame is 
immediately extinguished. This happens because of the absence of free 
oxygen, 

6. If the mouth of the bottle from which carbonic acid is escaping be 
held to that of another bottle, the gas can be poured into the second ves- 
sel, on account of its density being one-half greater than that of the air. 
Proof that the invisible gas has thus been transferred is had by placing 



* Chalk, marble, or salseratus, and chlorhydric (muriatic) acid, or etrong vine- 
gar (acetic acid) can be equally well employed. 



40 now CKors feed. 

ji burning- taper in the sccoiul bottle, when, if the experiment AViia rii^ht- 
ly condueted, the lliinie will bo extinguished. 

c. Into a bottle filled as in the last experiment ■with carbonic acid, 
some lime-water is poured and agitated. The iireviously clear lime-wa- 
ter immediately becomes turbid and milky from the formation of mrton- 
ate of lime, which is nearly insoluble iu water. 

Carbonic Acid in the Atmosphere— To show the pres- 
ence of carbonic acid in the atniosphero, it is only neces- 
sary to expose lime-water in an open vessel. But a little 
time elapses before the liquid is covered with a white film 
of carbonate. As already stated, the average proportion 
of carbonic acid in the atmosphere is 6-100()0ths 
(1-lGOOth nearly) by weight, or 4-lOOOOths (l-2r)00th) 
by bulk. Its quantity varies somewhat, however. Among 
over 300 analyses made by De Saussure in Switzerland, 
Verver in Holland, Lewy in New Granada, and Gilni iu 
Austria, the extreme range was from 47 to 8G parts by 
weight in 100,000. 

Deportment of Carbonic Acid towards Water. — Water 
dissolves carbonic acid to a greater or less extent, accord- 
ing to the temperature and pressure. Under the best or- 
dinary conditions it takes up about its own volume of the 
gas. At the freezing point it may absorb nearly twice as 
much. This gas is therefore usually found in spring, well, 
and river waters, as well as in dew and rain. The consid- 
erable amount held in solution in cold springs and wells 
is a principal reason of the refreshing quality of their wa- 
ter. Under pressure the proportion of carbonic acid ab- 
sorbed by water is much larger, and when the pressure is 
removed, a portion of the gas escapes, resuming its gase- 
ous form and causing effervescence. The liquid that flows 
from a soda-fountain is an aqueous solution of carbonic 
acid, made under pressure. Bottled cider, ale, champagne, 
and all effervescent beverages, owe their sparkle and nuich 
of their refreshing qualities to the carbonic acid they con- 
tahi. 



ATMOSPMEllIC AIIl AS THE FOOD OF PLANTS. 41 

The Absorption of Carbonic Acid by Plants. — In 1771 
Priestley, in England, found that the leaves of plants im- 
mersed in water, sometimes disengaged carbonic acid, 
sometimes oxygen, and sometimes no gas at all. A few 
years later Ingenhouss proved that the exhalation of car- 
bonic acid takes place in the absence, and that of oxygen 
in the presence, of solar light. Several years more elapsed 
before Sennebier first deihonstrated that the oxygen which 
is exhaled by foliage in the sunlight comes from the car- 
bonic acid contained in the water in which the plants are 
immersed for tlie purpose of these experiments. It had 
been already noticed, by Ingenhouss, that in s^^ring water 
plants evolve more oxygen than in river water. We now 
know that the former contains more carbonic acid than the 
latter. Where the water is by accident or 2)urposcly fiee 
from carbonic acid, no gas is evolved by foliage in the 
sunlight. 

The attention of scientific men was greatly attracted 
by these interesting discoveries ; and shortly Percival, in 
England, found that a plant of mint whose roots were 
stationed in water, flourished better when the air bathing 
its foliage was artificially enriched in carbonic acid than in 
the ordinary atmosphere. 

In 1840 Boussingault furnished direct proof, of what 
indeed was hardly to be doubted, viz.: the absorption of 
the carbonic acid of the atmosphere by foliage. 

Into one of the orifices in a thrcc-nccked glass globe he introduced 
and fixed air-tight tlie branch of a living vine bearing twenty leaves; 
with another opening he connected a tnbe through which a slow current 
of air, containing, in one experiment, four-lOOOOths of carbonic acid, 
could be passed into the globe. This air after streaming over the vine 
leaves, at the rate of about 15 gallons ]icr hour, escaped by the third 
neck into an arrangement for collecting and Avcighing the carbonic acid 
that remained in it. The experiment being set in process in the sun- 
light, it was found that the enclosed foliage removed from the current 
of air three-fourths of the carbonic acid it at first contained. 

Influence of the Relative Quantity of Carbonic Acid. — 

De Saussure investigated the influence of various projior- 



42 HOW CROPS FEED. 

tions of carbonic acid mixed with atmospheric air on the 
development of vegetation. He found that young peas (4 
inches high) when exposed to direct sunlight, endured for 
some days an atmosphere consisting to one-half of carbonic 
acid. When the proportion of this gas was increased to 
two-thirds or more, they speedily withered. In air con- 
taining one-twelfth of carbonic acid the peas flourished 
much better than in ordinary atniosj^heric air. The aver- 
age increase of each of the plants exposed to the latter 
for five or six hours daily during ten days was §ight 
grains ; while in the former it amounted in the same time to 
eleven grains. In the shade, however, Saussure found that 
increase of the proportion of carbonic acid to one-twelfth 
was detrimental to the plants. Their growth under these 
circumstances was but three-fifths of that experienced by 
similar plants exposed to the same light for the same time, 
but in common air. He also proved that foliage cannot long 
exist in the total absence of carbonic acid, when exposed 
to direct sunlight. This result was obtained by enclosing 
young plants whose roots were immersed in water, or the 
branches of trees stationed in the soil, in a vessel which 
contained moistened quicklime. This substance rapidly 
absorbs and fixes carbonic acid, forming carbonate of lime. 
Thus situated, the leaves began in a few days to turn yel- 
low, and in two to three weeks they dropped ofi*. 

In darkness the presence of lime not only did not de- 
stroy the plants, but they j^rospered the better for its 
presence, i. e., for the absence or constant removal of car- 
bonic acid. 

Boussingault has lately shown that pure carbonic acid 
is decomposed by leaves exposed to sunlight with extreme 
slowness, or not at all. It must be mixed with some other 
gas, and when diluted with either oxygen, nitrogen, or hy- 
drogen, or even when rarefied by the air-pump to a certain 
extent, the absorption and decomposition proceed as usual. 

Conclusion. — It thus is proved 1st, that vegetation 



ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 43 

can flourish only when its foliage is bathed by an atmos- 
phere which contains a certain small amount of carbonic 
acid ; 2d, that this gas is absorbed by the leaves, and, un- 
der the influence of sunlight, is decomposed within the 
plant, its carbon being retained, and in an unknown man- 
ner becoming a part of the plant itself, wliile the oxygen 
is exhaled into the atmosphere in the free state. 

Relative volumes of absorbed Carbonic Acid and ex- 
haled Oxygen. — From the numerous experiments of De 
Saussure, and from similar ones made recently with greatly 
improved means of research by linger and Knop, it is es- 
tablished that in sunlight the volume of oxygen exhaled 
is nearly equal to the volume of carbonic acid absorbed. 
Since free oxygen occupies the same bulk as the carbonic 
acid j)roduced "by uniting it with carbon, it is evident that 
carbon mainly and not oxygen to much extent, is retained 
by the plant from this source. 

Respiration and Fixation of Carbon by Plants. — In 
1851 Garreau, and in 1858 Corenwinder, reviewed experi- 
mentally the whole subject of the relations of plants to 
carbonic acid. Their researches fully confirm the conclu- 
sions derived from older investigations, and furnish some 
additional facts. 

We have already seen (p. 22) that the plant requires 
free oxygen, and that this gas is absorbed by those parts 
of vegetation which are in the act of growth. As a con- 
sequence of this entrance of oxygen into the plant, a cor- 
responding amount of carbonic acid is produced within 
and exhales from it. There go on accordingly, in the ex- 
panding plant, two opposite processes, viz., the absorption 
of oxygen and exhalation of carbonic acid, and the ab- 
sorption of carbonic acid and evolution of oxygen. The 
first process is chemically analogous with the breathing 
of animals, and may hence be designated as respiration. 
We may speak of the other process as the fixation of 
carbon. 



44 HOW CROPS FEED. 

These opposite changes obviously cannot take place at 
the same points, but must proceed in different organs or 
cells, or in different parts of the same cells. They further- 
more tend to counterbalance each other in their effects on 
the atmosphere surrounding the plant. The processes to 
which the absorption of oxygen and evolution of carbonic 
acid are necessary, appear to go on at all hours of the day 
and night, and to be independent of the solar liglit. The 
production of carbonic acid is then continually occurring ; 
but, under the influence of the sun's direct rays, the oppo- 
site absorption of carbonic acid and evolution of oxygen 
proceed so much more rapidly, that when we experiment 
with the entire plant the first result is completely masked. 
In our experiments we can, in fact, only measure the pre- 
ponderance of the latter process over the former. In sun- 
light it may easily happen that the carbonic acid which 
exhales from one cell is instantly absorbed by another, and 
likewise the oxygen, which escapes from the latter, may 
be in part imbibed by the former. 

In total darkness it is believed that carbonic acid is not 
absorbed and decomposed by the plant, but only produced 
in, and exhaled from it. In no case has any evolution of 
oxygen been observed in the absence of light. 

When, instead of being exposed to the direct rays of 
the sun, only the diffused light of cloudy days or the soft- 
ened light of a dense forest acts upon them, plants may, ac- 
cording to circumstances, exhale either oxygen or carbonic 
acid in preponderating quantity. In his earlier investiga- 
tions, Corenwinder observed an exhalation of carbonic acid 
in diffused light in the cases of tobacco, sunflower, lupine, 
cabbage, and nettle. On the contrary, he found that let- 
tuce, the pea, violet, fuchsia, periwinkle, and» others, evolv- 
ed oxygen under similar conditions. In one instance a 
bean exhaled neither gas. These differences are not pe- 
culiar to the plants just specified, but depend upon the in- 
tensity of the light and the stage of development in which 



ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 45 

the plant exists. Corenwinder noticed that the evolution 
of carbonic acid in diffused light was best exhibited by 
very young plants, and mostly ceased as they grew older. 

Corenwinder has confirmed and extended these observa- 
tions in more recent investigations. (Ann. d. /Scl. JVat., 
1864, I, 297.) 

He finds that buds and young leaves 'exhale carbonic 
acid (and absorb oxygen) by day, even in bright sunshine. 
He also finds that all leaves exhale carbonic acid not alone 
at night, but likewise by day, when placed in the diffused 
light of a room, illuminated from only one side. A j^lant, 
which in full light yields no carbonic acid to a slow stream 
of air passing its foliage, immediately gives off the gas 
when carried into such an apartment, and vice versa. 

Amount of Carbonic Acid absorbed. — The quantity of 
carbonic acid absorbed by day. in direct light is vastly 
greater than that exhaled during the night. According 
to Coren winder's experiments, 15 to 20 minutes of direct 
sunlight enable colza, the pea, the raspberry, the bean, 
and sunflow^er, to absorb as much carbonic acid as they 
exhale during a whole night. 

As to the amount of carbonic acid whose carbon is re- 
tained, Corenwinder found that a single colza i^lant took 
up in one day of strong sunshine more than two quarts of 
the gas. 

Boussingault (Comptes Rend.^ Oct. 23d, 1865) found as 
the average of a number of experiments, that a square me- 
ter of oleander leaves decomposed in sunlight 1.108 liters 
of carbonic acid per hour. In the dark, the same surface 
of leaf exhaled but 0.07 liter of this gas. 

Composition of the Air within the Plant. — Full con- 
firmation of the statements above made is furnished by 
tracing the changes which take place within the vegeta- 
ble tissues. Lawes, Gilbert, and Pugh, {Phil. Trans.., 
1861, II, p. 486,) have examined the composition of the 



46 



HOW CROPS FEED. 



air contained in plants, as well when the latter are remov- 
ed from, as when they are subjected to, the action of light. 
To collect the gas from the plants, the latter were placed 
in a glass vessel filled with water, from which all air had 
been expelled by long boiling and subsequent cooling in 
full and tightly closed bottles. The vessel was then con- 
nected with a simple apparatus in which a vacuum was 
produced by the fall of mercury, down a tube of 30 inches 
height. The air contained within the cells of the plant 
was thus drawn over into the vacuum and collected for 
examination. We give some of the results of the 6th 
series of their examinations. "The Table shows the 
Amount and Composition of the Gas evolved into a Tor- 
ricellian vacuum by duplicate portions of oat-plant, both 
kept in the dark for some time, and then one exposed to 
sunlight for about twenty minutes, when both were sub- 
mitted to exhaustion." 











Per cent. 


Bate, 

1858. 


Conditions 

during 
Exhaustion. 


Cubic centimeters 

of 

Gas collected. 


Nitrogen. 


Oxygen. 


Carbonic Acid. 


July 31. 
Aug. 2. 
Aug. 2. 


( In dark. 
\ In sunlight. 
J In dark. 
j In sunlight. 
j In dark. 
( In sunlight. 


24.0 
34.5 
10.6 
39.2 
30.7 
26.5 


77.08 
68.69 
68.28 
67.86 
76.87 
69.43 


3.75 
24.93 
10.21 
25.95 

8.14 
27.17 


19.17 
6.38 

21.51 
6.89 

14.99 
3.40 



These analyses show plainly what it is that happens in 
the cells of the plant. The atmospheric air freely pene- 
trates the vegetable tissues, (H. C. G., p. 288.) In dark- 
ness, the oxygen that is thus contained within the plant 
takes carbon from the vegetable matter and forms with it 
carbonic acid. This process goes on with comparative 
rapidity, and the proportion of oxygen may be diminish- 
ed from 21, the normal percentage, to 4, or even, as in 
some other experiments, to less than 1 per cent of the 
volume of the air. Upon bringing the vegetable tissue 
into sunlight, the carbonic acid previously formed within 
the cells undergoes decomposition, with separation of its 



ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 47 

oxygen in the free gaseous condition, while its carbon re- 
mains in the solid state as a constituent of the plant. Re- 
ferring to the table above, we see that twenty minutes' 
exposure to the solar rays was sufficient in the second ex- 
periment (where the proportion of nitrogen remained 
nearly unaltered) to decompose 14 per cent of carbonic acid 
and liberate its oxygen. The total volume of air collected 
was 2.4 cubic inches, and the volume of decomposed car- 
bonic acid was ^ of a cubic inch, that of the liberated 
oxygen being the same. 

Supply of Carbonic Acid in the Atmosphere. — Although 
this body forms but toooo of the weight of the atmosphere, 
yet such is the immense volume of the latter that it is cal- 
culated to contain, when taken to its entire height, no less 
than 3,400,000,000,000 tons of carbonic acid. This 
amounts to about 28 tons over every acre of the earth's 
surface. 

According to Chevandier, an acre of beech-forest annu- 
ally assimilates about one ton (1950 lbs.) of carbon, an 
amount equivalent to 3^ tons of this gas. Were the whole 
earth covered with this kind of forest, and did it depend 
solely upon the atmosphere for carbon, eight years must 
elapse before the existing supply would be exhausted, in 
case no means had been provided for restoring to the air 
what vegetation constantly removes. 

When we consider that but one-fourth of the earth's 
surface is land, and that on this the annual vegetable pro- 
duction is very far below (not one-third) the amount stat- 
ed above for thrifty forest, we are warranted in assuming 
the atmospheric content of carbonic acid sufficient, with- 
out renewal, for a hundred years of growth. This ingredi- 
ent of the atmosphere is maintained in undiminished 
quantity by the oxidation of carbon in the slow decay of 
organic matters, in the combustion of fuel, and in animal 
respiration. 

That the carbonic acid of the atmosphere may fully suf- 



48 now CROPS feed 

fioo to provide a rapidly growing vegetation with carbon 
is demonstrated by numerous facts. Here we need only 
mention that in a soil totally destitute of all carbon, be- 
sides that contamed in the seeds sown in it, Boussingault 
brought sunflowers to a normal development. The writer 
has done the same with buckwheat ; and Sachs, Knop, 
Stohmann, Xobbe and Siegert, and others, have produced 
perfect plants of maize, oats, etc., whose roots, throughout 
the whole period of growth, were immersed in a weak, 
saline solution, destitute of carbon. (See H. C. G., Water 
Culture, p. 167.) 

Hellriegel's recent experiments give the result that the 
atmosplieric supply of carbonic acid is probably suflicient 
for the production of a maximum crop under all circum- 
stances ; at least artificial supply, whether of the gas, of 
its aqueous solution, or of a carbonate, to the soil, had no 
effect to increase the crop. {Chem. Ackersmann^ 1S68, 
p. IS.) 

Liebig considers carbonic acid to be, under all circum- 
stances, the exclusive source of the carbon of agricultural 
vegetation. To this point we shall recur in our study of 
the soil. 

Carbon fixed l>y f hlorophyll. — ^The fixation of carbon 
from the carbonic acid of the air is accomplished in, or has 
an intimate relation with, the chlorophyll gniins of the 
leaf or green stem. This is not only evident from the 
microscopic study of the development of the carbohy- 
drates, especially starch, whose organization proceeds from 
the chlorophyll, but is an inference from the experiments 
of Gris on the efi'ects of withholding iron from plants. In 
absence of iron, the leaf may unfold and attain a certain 
development ; but chlorophyll is not formed, and the plant 
soon dies, without any real growth by assimilation of food 
from without. (H. C. G., p. 200.) Finally, experiment 
shows that oxygen is given off" (and carbonic acid decom- 
posed with fixation of carbon) only from those parts of 



ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 49 

plants in which the microscope reveals chlorophyll, although 
the prevailing color may be other than green. 

Influence of Lij^ht on Fixation of Carbon.— As men- 
tioned, Ingenhouss (in 1779) discovered that oxygen gas 
is given off from foliage, and carbon fixed in the plant 
only under the influence of light. Experiments show that 
when a seed germinates in exclusion of light it not only 
does not gain, but steadily loses weight from the consump- 
tion of carbon (and hydrogen) in slow oxidation (respira- 
tion). 

Thus Boussingault (Comptes Bendus^ 1864, p. 883) 
caused two beans to germinate and vegetate, one in the 
ordinary liglit and one in darkness, during 26 days. The 
gain in light and loss in darkness in entire (dry) weight, 
and of carbon, etc., are seen from the statement below. 

In Light. In Darkness. 

Weight of seed 0.933 gnira 0.936 gram. 

Weight of plant 1.393 " 0.5GG " 



Gain 


= 0.371 gram. 


Loss. 


...0.300 gram. 


Carbon, Gain 


= 0.193G " 


Loss., 


..0.159S " 


Hydrogen, " 


= 0.0300 " 


" ., 


..0.0333 " 


Oxygen, " 


= 0.1591 " 


u 


..O.ITGG " 



§6. 

THE AMMONIA OF THE ATMOSPHERE AND ITS RELATIONS 
TO VEGETABLE NUTRITION. 

Ammonia is a gas, colorless and invisible, but having a 

peculiar pungency of odor and an acrid taste. 

Preparation.— It may he obtained in a state of purity by heat- 
ing a mixture of chloride of ammonium (sal ammoniac) and quicklime. 
Equal quantities of the two substances just named (50 grams of cacli) 
are separately pulverized, introduced into a llask, and well mixed by 
shaking. A straiglit tube 8 inches long is now secured in the neck of 
the flask by means of a perforated cork, and heat applied. The ammonia 
gas which soon escapes in abundance is collected in dr\' bottles, which 
are inverted over the tube. The gas, rapidly entering the bottle, in a 
few moments displaces the twice heavier atmospheric air. As soon as a 

3 



50 HOW CROPS FEED. 

feather wet with vinej^ar or dilute elilorhycli-ic acid becomes surrounded 
Avith a dense smoke when approached to the mouth of the bottle, the 
latter may be removed, corked, and another put in its place. Three or 
four pint bottles of gas thus collected will serve to illustrate its proper- 
ties, as shortly to be noticed. 

Solubility in Water. — This character of ammonia is ex- 
hibited by removing, under cold water, the stopper of a 
bottle filled with the gas. The water rushes with great 
violence into the bottle as into a vacuum, and entirely fills 
it, provided all atmospheric air had been displaced. 

The aqua ammonia, or spirits of hartshorn of the drug- 
gist, is a strong solution of ammonia, prepared by passing 
a stream of ammonia gas into cold water. At the freez- 
ing point, water absorbs 1,150 times its bulk of ammonia. 
When such a solution is warmed, the gas escapes abund- 
antly, so that, at ordinary summer temperatures, only one- 
half the ammonia is retained. If the solution be heated 
to boiling, all the ammonia is expelled before the water has 
nearly boiled away. The gas escapes even from very di- 
lute solutions when they are exposed to the air, as is at 
once recognized by the sense of smell. 

Composition. — When ammonia gas is heated to redness 
by being made to pass through an ignited tube, it is de- 
composed, loses its characteristic odor and other proper- 
ties, and is resolved into a mixture of nitrogen and hydro- 
gen gases. These elements exist in ammonia in the pro- 
portion of one part by bulk of nitrogen, to three parts of 
hydrogen, or by weight fourteen j^arts or one ktom of 
nitrogen and three parts, or three atoms of hydrogen. 
The subjoined scheme exhibits the composition of ammo- 
nia, as expressed in symbols, atoms, and percentages. 
Symbol. At vPt. Per cent. 

N = 14 .. 83.39 

H, = 3 .. 17.61 



NH3 = 17 .. 100.00 

Formation of Ammonia. — 1. When hydrogen and ni- 
trogen gases are mingled together in the proportions to 



ATMOSPHERIC AIR AS THE POOD OF PLANTS. 51 

form ammonia, they do not combine either spontaneously or 
by aid of any means yet devised, but remain for an indef- 
inite period as a mere mixture. The oft repeated assertion 
that nascent hydrogen, i. e., hydrogen at the moment of 
liberation from some combination, may unite with free 
nitrogen to form ammonia, has been completely refuted by 
the experiments of Will, {Ann. Ch. n. Ph., XLV, 110.) 
The ammonia observed by older experimenters existed, 
ready formed, in the materials they operated with. 

2. It appears from recent researches (of Boettger, 
Schonbein, and Zabelin) that ammonia is formed in minute 
quantity from atmospheric nitrogen in many cases of com- 
bustion, and is also generated when vapor of water and 
the air act upon each other in contact with certain organic 
matters, at a temperature of 120° to 160° F. To this sub- 
ject we shall again recur, p. 77. 

3. Ammonia may result from the reduction of nitrous 
and nitric acids, and from the action of alkalies and lime 
upon the albuminoids, gelatine, and other similar organic 
matters. To these modes of its formation we shall recur 
on subsequent pages. 

4. Ammonia is most readily and abundantly formed from 
organic nitrogenous bodies; e. g., the albuminoids and 
similar substances, by decay or by dry distillation. It is 
supposed to have been called ammonia because one of its 
most common compounds (sal ammoniac) was first prepared 
by burning camels' dung near the temple of Jupiter Amnion 
in Libya, Asia Minor. The name hartshorn, or spirits of 
hartshorn, by which it is more commonly known, was 
adopted from the circumstance of its prej)aration by dis- 
tillino: the horns of the staoj or hart. 

The ammonia and ammoniacal salts of commerce (car- 
bonate of ammonia, sal ammoniac, and sulphate of ammo- 
nia) are exclusively obtained from these sources. 

When urine is allowed to become stale, it shortly smells 



63 HOW CEOPS FEED. 

of ammonia, which copiously escapes in the form of car- 
bonate, and may be separated by distillation. 

When bones are heated in close vessels, as in the manu- 
facture of bone-black or bone-char for sugar refining, the 
liquid product of the distillation is strongly charged with 
carbonate of ammonia. 

Commercial ammonia is mostly derived, at present, from 
the distillation of bituminous coal, and is a bye-product of 
the manufacture of illuminating gas. The gases and va- 
pors that issue from the gas-retort in which the coal is heat- 
ed to redness, are washed by passing through water. This 
wash water is always found to contain a small quantity of 
ammonia, which may be cheaply utilized 

The exhalations of volcanoes and fumeroles likewise 
contain ammonia, which is probably formed in a similar 
manner. 

In the processes of combustion and decay the elements 
of the organic matters are thrown into new groupings, 
which are mostly simpler in composition than the original 
substances. A portion of nitrogen and a corresponding 
portion of hydrogen then associate themselves to form am- 
monia. 

Ammonia is a Stroai? Alkaline Base.— Those bases 
which have in general the strongest affinity for acids, are 
potash, soda, and ammonia. These bodies are very similar 
in many of their most obvious characters, and are collec- 
tively denominated the alkalies. They are alike freely 
soluble in water, have a bitter, burning taste, alike corrode 
the skin and blister the tongue ; and, united with acids, 
form the most permanent saline compounds, or salts. 

Carbonate of Ammonia. — If a bottle be filled with car- 
bonic acid, (by holding it inverted over a candle until the 
latter becomes extinguished when passed a little way into 
the bottle,) and its mouth be applied to that of a vessel 
containing ammonia gas, the two invisible airs at once 



ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 53 

combine to a solid salt, the carbonate of ammonia, which 
appears as a white cloud where its ingredients come in 
contact. 

Carbonate of ammonia occurs in commerce under the 
name "salts of hartshorn," and with the addition of some 
perfume forms the contents of the so-called smelling-bot- 
tles. It rapidly vaporizes, exhaling the odor of ammonia 
very strongly, and is hence sometimes termed sal volatile. 
Like camphor, this salt passes from the solid state into 
that of invisible vapor, at ordinary temperatures, without 
assuming intermediately the liquid form. 

In the atmosphere the quantity of carbonic acid greatly 
preponderates over that of the ammonia ; hence it is im- 
possible that the latter should exist in the free state, and 
we must assume that it occurs there chiefly in combination 
witli carbonic acid. The carbonate of ammonia, whether 
solid or gaseous, is readily soluble in water, and like free 
ammonia it evaporates from its solution with the first 
portions of aqueous vapor, leaving the residual water rel- 
atively free from it. 

In the guano-beds of Peru and Bolivia, carbonate of 
ammonia is sometimes found in the form of large trans- 
parent crystals, which, like the artificially-prepared salt, 
rapidly exhale away in vapor, if exposed to the air. 

This salt, commonly called bicarbonate of ammonia, con- 
tains in addition to carbonic acid and ammonia, a portion 
of water, which is indispensable to its existence. Its com- 
position is as follows : 

' Symbol. At. w't Per cent. 
NH3 17 21.5 

H2O 18 22.8 

CO2 41 55.7 

. NH3. H2O. CO2. 79 100.0 

Tests ibr AmmouinL. — a. If salts of ammonia are rubbed to- 
jj^ether with slaked lime^ best with the addition of a few drops of water, 
the ammonia is liberated in the gaseous state, and betrays itself (1) by 
its characteristic odor ; (2) by its readiQn on moistened test-papers ; and 



54 HOW CPwOPS FEED. 

(3) bj- giving rise to the formation of lohite fames, when any object {e. g., 
a glass rod) moistened with hydrochloric acid, is bronglit in contact with 
it. These fumes arise Irom the formation of solid ammoniacal salts j^ro- 
duced by the contact of the gases. 

6. Xessler's Test.— For the detection of exceedingly minute traces of 
ammonia, a reaction first pointed out by Ncssler may be employed. Di- 
gest at a gentle heat 2 grammes of iodide of potassium, and 3 grammes 
of iodide of mercury, in 5 cub. cent, of water; add 20 cub. cent, of wa- 
ter, let the mixture stand for some time, then filter; add to the filtrate 
SO cub. cent, of pure concentrated solution of potassa(l : 4); and, should 
a precipitate form, filter again. If to this solution is added, in small 
quantity, a liquid containing ammonia or an ammonia-salt, a reddish hrown 
'precipitate, or with exceedingly small quantities of ammonia, a yellow 
coloration is produced from the formation of dimercurammouic iodide, 
>sHgo I.OHa. 

c. BoJdig's Tcsi.— According to Bohlig, chloride of mercury (corrosive 
sublimate) is the most sensitive reagent for ammonia, when in the free 
state or as carbonate. It gives a white precijntate, or in very dilute so- 
lutions (even when containing but Maocooo of ammonia) a white turbidity, 
due to the separation of mercurammonie chloride, NHa Hg.Cl. In solu- 
tions of the salts of ammonia with other acids than carbonic, a clear 
solution of mixed carbonate of potassa and chloride of mercury must be 
employed, which is prepared by adding 10 drops of a solution of the 
purest carbonate of potassa, (1 of salt to 50 of water,) and 5 drops of a 
solution of chloride of mercury to 80 c. c. of water exempt from am- 
monia (such is the water of many springs, but ordinary distilled water 
rarely). This reagent may be kept in closed vessels for a time without 
change. If much more concentrated, oxide of mercury separates from it. 
By its use the ammonia salt is first converted into carbonate by double 
decomposition with the carbonate of potassa, and the further reaction 
proceeds as before mentioned. 

Occurrence of Ammonia in the Atmosphere. — The ex- 
istence of ammonia in the atmosphere was first noticed by 
De Saussure, and has been proved repeatedly by direct 
experiment. That the quantity is exceedingly minute has 
been equally well established. 

Owing partly to the variable extent to which ammonia 
occurs in the atmosphere, but chiefly to the difficulty of 
collecting and estimating such small amounts, the state- 
ments of those who have experimented upon this subject 
are devoid of agreement. 

We present here a tabulated view of the most trust- 
worthy results liitherto published : 



ATMOSPHERIC .AIE xiS THE POOD OF PLANTS. 55 

1,000,000,000 parts of atmospheric air contain of ammonia, according to 
Graeger, at Miililbausen, Germany, average, 333 parts. 
Fresenius, " Wiesbaden, " " 133 " 

Pierre, 
It 

Bineau, 



" Caen, France, 


1851-52, " 


3500 


u a u 


1853-53, " 


500 


" Lyons, " 


1852-53, 


250 


" Caluire, " 


" winter, 


40 


(( u u 


" summer. 


80 


" Paris, " 


1849-50, average. 


21 


" Grenelle, " 


1851, 


21 



Vine, 

Graham hns shown by experiment (Ville, Recherches 
sur la Vegetation^ Paris, 1853, p. 5,) that a quantity of 
ammonia like that found by Fresenius is sufficient to be 
readily detected by its effect on a red litmus paper, which 
is not altered in the air. This demonstrates that the at- 
mosphere where Graham experimented (London) contained 
less than '^^Ij^^g^^^gg^ths of ammonia in the state of bicar- 
bonate. The experiments of Fresenius and of Griiger 
were made with comparatively small volumes of air, and 
those of the latter, as \yq\\ as those of Pierre, and some of 
Bineau's, were made in the vicinity of dwellings, or even 
in cities, where the results might easily be influenced by 
local emanations. Bineau's results were obtained by a 
method scarcely admitting of much accuracy. 

The investigations of Ville {Recherches^ Paris, 1853,) 
are, perhaps, the most trustworthy, having been made on 
a large scale, and apparently with every precaution. We 
may accordingly assume that the average quantity of am- 
monia in the air is one part in fifty millions, although the 
amount is subject to considerable fluctuation. 

From the circumstance that ammonia and its carbonate 
are so readily soluble in water, we should expect that in 
rainy weather the atmosphere would be washed of its am- 
monia ; while after prolonged dry weather it would con- 
tain more than usual, since ammonia escapes from its 
solutions with the first portions of aqueous vapor. 

The Absorption of Ammonia by Vegetation.— The gen- 
eral fact that ammonia in its compounds is appropriated 



56 



HOW CROPS FEED 



by plants as food is most abundantly established. The 
salts of ammonia applied as manures in actual farm prac- 
tice have produced the most striking effects in thousands 
of instances. 

By watering potted plants with very dilute solutions of 
ammonia, their luxuriance is made to surpass by far that 
of similar plants, which grow in precisely the same condi- 
tions, save that they are supplied with simple water. 

Ville has stated, 1851-2, that vegetation in conservn- 
toiies may be remarkably promoted by impregnating the 
air Avith gaseous carbonate of ammonia. For this purpose 
lumps of the solid salt are so disposed on the heating ap- 
paratus of the green-honse as to gradually vaporize, or 
vessels containing a mixture of quicklime and sal ammo- 
niac may be employed. Care must be taken that the air does 
not contain at any time more than four ten-thousandths 
of its weight of the salt ; otherwise the foliage of tender 
plants is injured. Like results were obtained by Petzholdt 
and Chlebodarow in 1852-3. 

Absorption of Ammonia by Foli- 
age. — ^Although such facts indicate 
that ammonia is directly absorbed by 
foliage, they fail to prove that the 
soil is not the medium through Avhich 
the absorption really takes j^lace. We 
remember that accordinor to Unojer 
and Duchartre water enters the 
higher plants almost exclusively by 
the roots, after it has been absorbed 
by the soil. To Peters and Sachs 
( Chem. AcJcersmcmn^ 6, 158) we owe 
an experiment which appears to de- 
monstrate that ammonia, like carbonic 
acid, is imbibed by the leaves of 
plants. The figure represents the ap- 
paratus employed. It consisted of a glass bell, resting below, 




ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 57 

air-tight, upon a gla^s plate, and having two glass tubes 
cemented into its neck above, as in fig. 6. Through 
an aperture in the centre of the glass plate the stem of 
the plant experimented on was introduced, so that its fo- 
liage should occupy the bell, while the roots were situated 
in a pot of earth beneath. Two young bean-plants, grow- 
ing in river sand, were arranged, each in a separate appa- 
ratus, as in the figure, on June 19th, 1859, their stems be- 
ing cemented tightly into the opening below, and through 
the tubes the foliage of each plant received daily the same 
quantities of moist atmospheric air mixed with 4-5 per 
cent of carbonic acid. One plant was supplied in addition 
with a quantity of carbonate of ammonia, which was in- 
troduced by causing the air that was forced into the bell 
to stream through a dilute solution of this salt. Both 
plants grew well, until the experiment was terminated, on 
the 11th of August, when it was found that the plant 
whose foliage was not supplied with carbonate of ammo- 
nia weighed, dry, 4.14 gm., while the other, which was 
supplied with the vapor of this salt, weighed, dry, 6.74 
gms. The first plant had 20 full-sized leaves and 2 side 
shoots ; the second had 40 leaves and 7 shoots, besides a 
much larger mass of roots. The first contained 0.106 
gm. of nitrogen ; the second, double that amount, 0.208 
gm. Other trials on various plants failed from the diffi- 
culty of making them grow in the needful circumstances. 

The absorption of ammonia by foliage does not appear, 
like that of carbonic acid, to depend upon the action of 
sunlight ; but, as Mulder has remarked,* may go on at 
all times, especially since the juices of plants are very fre- 
quently more or less charged with acids which directly 
unite chemically with ammonia. 

When absorbed, ammonia is chiefly applied by agricul- 



♦ Cheraie der Ackerkrume, Vol. 2, p. 211. 

3* 



58 HOW CROPS FEED. 

tural plants to the production of the albuminoids.* We 
measure the nutritive effect of ammonia salts applied as 
fertilizers by the amount of nitrogen which vegetation as- 
similates from them. 

Effects of Ammonia on Vegetation. — The remarkable 
effect of carbonate of ammonia upon vegetation is well 
described by Ville. We know that most plants at a cer- 
tain period of growth under ordinary circumstances cease 
to produce new branches and foliage, or to expand those 
already formed, and begin a new phase of development in 
providing for the perpetuation of the species by producing 
flowers and fruit. If, however, such plants are exposed 
to as much carbonate of ammonia gas as they are capable 
of enduring, at the time when flowers are beginning to 
form, these are often totally checked, and the activity of 
growth is transferred to stems and leaves, which assume 
a new vigor and multiply with extraordinary luxuriance. 
If flowers are formed, they are sterile, and yield no seed. 

Another noticeable effect of ammonia — one, however, 
which it shares with other substances — is its power of deep- 
ening the color of the foliage of plants. This is an indi- 
cation of increased vegetative activity and health, as a 
pale or yellow tint belongs to a sickly or ill-fed growth. 

A third result is that not only the mass of vegetation 
is increased, but the relative proportion of nitrogen in it is 
heiglitened. This result was obtained in the experiment of 
Peters and Sachs just described. To adduce a single other 
instance, Yille found that grains of wheat, grown in pure 
air, contained 2.09 per cent of nitrogen, while those which 
were produced under the influence of ammonia contained 
3.40 per cent. 



* In tobacco, to th3 production of nicotine ; in coffee, of caffeine ; and in many 
other plants to analogous eubstances. Plants appear oftentimes to contain 
small quantities of ammonia salts and nitrates, as well as of asparagin, (C4 Hs 
N2 O3,) a substance first found in asparagus, and which is formed in many 
plants when tliey vegetate in exchision of light. 



ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 59 

Do Healthy Plants Exhale Ammonia ?— The idea having 
been advanced that in the act of vegetation a loss of ni- 
trogen may occur, possibly in the form of ammonia, Knop 
made an experiment Avith a water-plant, the Typha lati- 
folia^ a species of Cat-tail, to determine this point. The 
plant, growing undisturbed in a pond, was enclosed in a 
glass tube one and a half inches in diameter, and six feet 
long. The tube was tied to a stake driven for the purpose ; 
its lower end reached a short distance below the surface 
of the water, while the upper end was covered air-tight 
with a cap of India rubber. This cap was penetrated by 
a narrow glass tube, which communicated with a vessel 
filled with splinters of glass, moistened with pure hydro- 
chloric acid. As the large tube was placed over the plant, 
a narrow U-shaped tube was immersed in the water to 
half its length, so that one of its arms came within, 
and the other without, the former. To the outer extremity 
of the U-tube was attached an apparatus, for the perfect 
absorption of ammonia. By aspirating at the upper end 
of the long tube, a current of ammonia-free air was thus 
made to enter the bottom of the apparatus, stream upward 
along the plant, and pass through the tube of glass-splint- 
ers wet with hydrochloric acid. Were any ammonia 
evolved within the long tube, it would be collected by the 
acid last named. To guard against any ammonia that 
possibly might arise from decaying matters in the water, 
a thin stratum of oil was made to float on the water with- 
in the tube. Through this arrangement a slow stream of 
air was passed for fifty hours. At the expiration of that 
time the hydrochloric acid was examined for ammonia ; 
but none was discovered. Our tests for ammonia are so 
delicate, that we may well assume that this gas is not ex- 
haled by the Typha latlfolia. 

The statements to be found in early authors (Sprengel, 
Schtibler, Johnston), to the efiect that ammonia is exhaled 
by some plants, deserve further examination. 



60 IIOAV CROPS FEED. 

The Chenopodlum vulvar la exhales from its foliage a 
body chemically related to ammonia, and that has been 
mistaken for it. This substance, known to the chemist as 
trimethylamine, is also contained in the flowers of Cra- 
taegus oxycantha, and is the cause of the detestable odor 
of tliese plants, which is that of putrid salt fish.* (Wicke, 
Liehlg's Ann., 124, p. 338.) 

Certain fungi (toad-stools) emit trimethylamine, or some 
analogous compound. (Lehmann, Sacks' Experimental 
Physiologie der Pflanzen, p. 273, note.) 

It is not impossible that ammonia, also, may be exhaled 
from these plants, but we have as yet no proof that such 
is the case. 

Ammonia of the Atmospheric Waters. — The ammonia 
proper to the atmosphere has little eifect upon plants 
through their foliage when they are sheltered from dew 
and rain. Such, at least, is the result of certain experi- 
ments. 

Boussingault (Agronomie, Ch'inile Agricole, et Physi- 
ologie, T. I, p. 141) made ten distinct trials on lupins, 
beans, oats, wheat, and cress. The seeds were sown in a 
soil, and the plants were watered with water both exempt 
from nitrogen. The plants were shielded by glazed cases 
from rain and dew, but had full access of air. The result 
of the ten experiments taken together was as follows : 

Wcigbt of seeds 4.965 grin's. 

" " dry harvest 18.730 " 

Nitrogen in harvest and soil.. .2499 " 
" " seeds 2307 " 

Gain of uitrogeu 0192 grm's = 7.6 per cent of the 

total quantity. 
When rains fall, or dews deposit upon the surface of the 

* Trimethylamine CaHciN = N (01X3)3 may be viewed as ammonia NII3, in 
which the three atoms of hydrogou are replaced by three atoms of methyl 
CH3. It is a jras like ammonia, and has its pun-rency, but accompanied with the 
odor of stale fish. It is prepared from herring pickle, and used in medicine un- 
der the name propylamine. 



ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 61 

soil, or upon the foliage of a cultivated field, they bring 
down to the reach of vegetation in a given time a quantity 
of ammonia, far greater than what is diifased throughout 
the limited volume of air which contributes to the nour- 
ishment of plants. The solubility of carbonate of ammo- 
nia in water has already been mentioned. In a rain-fall 
we have the atmosphere actually washed to a great de- 
gree of its ammonia, so that nearly the entire quantity of 
this substance which exists between the clouds and the 
earth, or in that mass of atmosphere through which the 
rain passes, is gathered by the latter and accumulated 
within a small space. 

Proportion of Ammonia in Rain- water, etc. — The pro- 
portion of ammonia * which the atmospheric waters thus 
collect and bring down upon the surface of the soil, or 
upon the foliage of plants, has been the subject of inves- 
tigations by Boussingault, Bineau, Way, Knop, Bobiere, 
and Bretschneider. The general result of their accordant 
investigations is as follows : In rain-water the quantity of 
ammonia in the entire fall is very variable, ranging in the 
country from 1 to 33 ]>arts in 10 million. In cities tlie 
amount is larger, tenfold the above quantities having been 
observed. 

The first portions of rain that fall usually contain much 
more ammonia than the latter portions, for the reason that 
a certain amount of water sufiices to wash the air, and 
what rain subsequently falls only dilutes the solution at 
first formed. In a long-continued rain, the water that 
finally falls is almost devoid of ammonia. In rains of 
short duration, as well as in dews and fogs, which occasion- 
ally are so heavy as to admit of collecting to a sufiicient 
extent for analysis, the proportion of ammonia is greatest, 
and is the greater the longer the time that has elapsed 
since a previous precipitation of water. 

* In all quantitative statements rci^arding ammonia, Nil 3 is to be understood, 
andnotNn4 0. 



62 HOW CROPS FEED. 

Boussinscault found in the first tenth of a slow-fallinsj 
rain (24th Sept., 1853) 66 parts of ammonia, in the last 
three-tenths but 13 parts, to 10 million of water. In dew 
he found 40 to 62 ; in fog, 25 to 72 ; and in one extraordi- 
nary instance 497 parts in ten million. 

Boussingault found that the average proportion of am- 
monia in the atmospheric waters (dew and fogs included) 
which he was able to collect at Liebfrauenberg (near Stras- 
burg, France) from the 26th of May to the 8th of Nov. 
1853, was 6 parts in 10 million {Agronomie, etc., T. II, 
238). Knop found in the rains, snow, and hail, that fell at 
Moeckern, near Leipzig, from April 18th to Jan. 15th, 
1860, an average of 14 parts in 10 million. ( Versuchs- 
jStatlone?i, Vol. 3, p. 120.) 

Pincus and RoUig obtained from the atmospheric wa- 
ters collected at Insterburg, North Prussia, during the 12 
months ending with March, 1865, in 26 analyses, an average 
of 7 parts of ammonia in 10 million of water. The average 
for the next following 12 months was 9 parts in 10 million. 

Bretschneider found in the atmospheric waters collected 
by him at Ida-Marienhiitte, in Silesin, from April, 1865, to 
April, 1866, as the average of 9 estimations, 30 parts of 
ammonia in 10 million of water. In the next year the 
quantity w^as 23 parts in 10 million. 

In 10 million parts of rain-water, etc., collected at the 
following places in Prussia, were contained of ammonia — 
at Regenwalde, in 1865, 24; in 1867, 28; at Dabme, in 
1865, 17; at Kuschen, in 1865, 5|-; and in 1866, 7^ parts. 
(Freifs. Ann. d. Landwirthschaft, 1867.) The monthly 
averages fluctuated without regularity, but mostly within 
narrow limits. Occasionally they fell to 2 or 3 parts, once 
to nothing, and rose to 35 or 40, and once to 144 parts in 
10 million. 

Quantity of Ammonia per Acre Brought Down by Rain, 
etc. — In 1855 and '56, Messrs. Lawes & Gilbert, at Roth- 
amstead, England, collected on a large rain-gauge having 



ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 63 

a surface of -i-o\o of an acre, the entire rain-fall (dews, etc., 
included) for those years. Prof Way, at that time chem- 
ist to the Royal Ag. Soc. of England, analyzed the waters, 
and found that the total amount of ammonia contained in 
them was equal to 7 lbs. in 1855, and 9|- lbs. in 1856, for 
an acre of surface. These amounts were yielded by 
663,000 and 616,000 gallons of rain-water respectively. 

In the waters gathered at Insterburg during the twelve- 
month ending March, 1865, Pincus and Kollig obtained 
6.38 lbs. of ammonia per acre.. 

Bretschneider found in the waters collected at Ida-Ma- 
rienhiitte from April, 1865, to April, 1866, 12 lbs. of am- 
monia per acre of surface. 

The significance of these quantities may be most appro- 
priately discussed after we have noticed the nitric acid of 
the atmosphere, a substance whose functions towards vege- 
tation are closely related to those of ammonia. 

§ "r. 

OZONE. 

When lightning strikes the earth or an object near 
its surface, a person in the vicinity at once perceives a 
peculiar, co-called " sulphureous " odor, which must belong 
to something developed in the atmosphere by electricity. 
The same smell may be noticed in a room in which an 
electrical machine has been for some time in vigorous 
action. 

The substance which is thus produced is termed ozone^ 
from a Greek word signifying to smell. It is a colorless 
gas, possessing most remarkable properties, and is of the 
highest importance in agricultural science, although our 
knowledge of it is still exceedingly imperfect. 

Ozone is not known in a pure state free from other 
bodies ; but hitherto has only been obtained mixed with 



64 HOW CROPS FEED. 

several times its weight of air or oxygen.* It is entirely 
insoluble in water. It has, when breathed, an irritating 
action on the lungs, and excites coughing like chlorine gas. 
Small animals are shortly destroyed in an atmosphere 
charged with it. It is itself instantly destroyed by a heat 
considerably below that of redness. 

The special character of ozone that is of interest in 
connection with questions of agriculture is its oxidizing 
poioer. Silver is a metal which totally refuses to combine 
with oxygen under ordinary circumstances, as shown by 
its maintaining its brilliancy without symptom of rust or 
tarnish when exposed to pure air at common or at greatly 
elevated temperatures. When a slip of moistened silver 
is placed in a vessel the air of which is charged with 
ozone, the metal after no long time becomes coated with a 
black crust, and at the same time the ozone disappears. 

By the application of a gentle heat to the J^lackened 
silver, ordinary oxygen gas, having the properties already 
mentioned as belonging to this element, escapes, and the 
slip recovers its original silvery color. The black crust is 
in fact an oxide of silver (AgO,) which readily suffers de- 
composition by heat. In a similar manner iron, copper, 
lead, and other metals, are rapidly oxidized. 

A variety of vegetable pigments, such as indigo, litmus, etc., are 
speedily bleached by ozone. This action, also, is simply one of oxidation. 

Gorup-Besanez {Ann. Ch. u. Ph., 110, 86; also, Fhysiologische CJiemie) 
has examined the deportment of a number of organic bodies towards 
ozone. He finds that egg-albumin and casein of milk are rapidly altered 
by it, while flesh fibriu is unaflfected. 

Starch, the sugars, the organic acids, and fats, are, when pure, unaf- 
fected by ozone. In presence of (dissolved in) alkalies, however, they 
are oxidized with more or less rapidity. It is remarkable that oxidation 
by ozone takes place only in the presence of water. Dry substances are 
unaffected by it. 

The peculiar deportment towards ozone of certain volatile oils will be 
presently noticed. 



* Baby and Glaus {Ann. Ch. u. Ph., 2d Sup., p. 304) prepared a mixture of oxy- 
gen and ozone containing nearly 6 per cent of the latter. 



ATMOSPHEEIC AIR AS THE FOOD OF PLANTS. 65 

Tests for Ozone, — Certain phenomena of oxidation that are 
attended with changes of color serve for the recognition of ozone. 

"We have already seen (H. C. G.,p. 64) that starch, when brought in 
contact with iodine, at once assumes a deep blue or purple color. When 
the compound of iodine with potassium, known as iodide of potas- 
sium, is acted on by ozone, its potassium is at once oxidized (to pot- 
ash,) and the iodine is set free. If now paper be impregnated with a 
mixture of starch-paste and solution of iodide of potassium,* we have a 
test of the presence of ozone, at once miost characteristic and delicate. 

Such paper, moistened and placed in ozonousf air, is speedily turned 
blue by the action of the liberated iodine upon the starch. By the use 
of this test the presence and abundance of ozone in the atmosphere has 
been measured. 

Ozone is Actire Oxygen. — That ozone is nothing more 
or less than oxygen in a peculiar, active condition, is shown 
by the following experiment. When perfectly pure and 
dry oxygen is enclosed in a glass tube containing moist 
metallic silver in a state of fine division, it is jDossible by 
long-continued transmission of electrical discharges to 
cause the gaseous oxygen entirely to disappear. On heat- 
ing the silver, which has become blackened (oxidized) by 
the process, the original quantity of oxygen is recovered 
in its ordinary state. The oxygen is thus converted under 
the influence of electricity into ozone, which unites with 
the silver and disappears in the solid combination. 

The independent experiments of Andrews, Babo, and 
Soret, demonstrate that ozone has a greater density than 
oxygen, since the latter diminislies in volume when elec- 
trized. Ozone is therefore condensed oxygen^\ i. e., its 
molecule contains more atoms than the molecule of ordi- 
nary oxygen gas. 



* Mis 10 parts of starch with 200 parts of cold water and 1 part of recently 
fusetl iodide of potassium, by rubbing them together in a mortar ; then heat to 
boiling, and strain through hnen. Smear pure filter paper with this paste, and dry 
The paper should be perfectly white, and must be preserved in a well-stoppered 
bottle. 

t I. c., charged with ozone. 

X Recent observations by Babo and Clans, and by Soret, show that the density 
of ozone is one and a half times greater than that of oxygen. 



66 HOAV CROPS FEED. 

Allotropisna.— This occurrence of an element in two or even 
more forms is not without other illustrations, aud is termed Allotropism. 
Phosphorus occurs in two conditions, viz., red phosphorus, which crys- 
tallizes in rhombohedrons, and like ordinary oxygen is comparatively 
inactive in its aflanitles ; and colorless phosphorus, which crystallizes in 
octahedrons, and, like ozone, has vigorous tendencies to unite with other 
bodies. Carbon is also found in three allotropic forms, viz., diamond, 
plumbago, and charcoal, which differ exceedingly in their chemical and 
physical characters. 

Ozone Formed by Chemical Action. — Not only is ozone 
produced by electrical disturbance, but it has likewise 
been shown to originate from chemical action ; and, in 
fact, from the very kind of action which it itself so vig- 
orously manifests, viz., oxidation. 

When a clean stick of colorless phosphorus is placed at 
the bottom of a large glass vessel, and is half covered 
with tepid water, there immediately appear white vapors, 
which shortly fill the apparatus. In a little time the pe- 
culiar odor of ozone is evident, and the air of the vessel 
gives, with iodide-of-potassium-starch-paper, the blue color 
which indicates ozone. In this experiment ordinary oxy- 
gen, in the act of uniting with phosphorus, is partially 
converted into its active modification ; and although the 
larger share of the ozone formed is probably destroyed by 
uniting with phosphorus, a portion escapes combination 
and is recognizable in the surrounding air. 

The ozone thus developed is mingled with other bodies, 
(phosphorous acid, etc.,) which cause the white cloud. 
The quantity of ozone that appears in this experiment, 
though very small, — under the most favorable circum- 
stances but ^ |j3oo of the weight of the air, — is still sufficient 
to exhibit all the reactions that have been described. 

Schonbein has shown that various organic bodies which 
are susceptible of oxidation, viz., citric and tartaric acids, 
when dissolved in water and agitated with air in the sun- 
light for half an hour, acquire the reactions of ozone. 
Ether and alcohol, kept in partially filled bottles, also be- 
come capable of producing oxidizing efiects. Many of the 



ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 67 

vegetable oils, as oil of turpentine, oil of lemon, oil of 
cinnamon, linseed oil, etc., possess the property of ozoniz- 
ing oxygen, or at least acquire oxidizing properties when 
exposed to the air. Hence the bleaching and corrosion 
of the cork of a partially filled turpentine bottle. 

It is a highly probable hypothesis that ozone may be 
formed in many or even all cases of slow oxidation, and 
that although the chief part of the ozone thus developed 
must unite at once with the oxidable substance, a portion 
of it may diffuse into the atmosphere and escape immediate 
combination. 

Ozone is likewise produced in a variety of chemical re- 
actions, whereby oxygen is liberated from combination at 
ordinary temperatures. When water is evolved by gal- 
vanic electricity into free oxygen and free hydrogen, the 
former is accompanied with a small proportion of ozone. 
The same is true in the electrolysis of carbonic acid. So, 
too, when permanganate of potash, binoxide of barium, 
or chromic acid, is mixed with strong sulphuric acid, ox- 
ygen gas is disengaged which contains an admixture of 
ozone.* 

Is Ozone Produced by Vegetation ? — It is an interesting 
question whether the oxygen so freely exhaled from the 
foliage of plants under the influence of sunlight is accom- 
panied by ozone. Various experimenters have occupied 



* It appears probable tbat ozone is developed in all cases of rapid oxidation at 
high temperatures. This has been long suspected, and Meissner obtained strong 
indirect evidence of the fact. Since the above was written, Pincus has announ- 
ced that ozone is produced when hj'drogen burns in the air, or in pure oxygen 
gas. The quantity of ozone thus developed is sufficient to be recognized by the 
odor. To observe this fact, a jet of hydrogen should issue from a fine orifice and 
burn with a small flame, not exceeding %-inch in length. A clean, dry, and cold 
beaker glass is held over the flame for a few seconds, when its contents will smell 
as decidedly of ozone as the interior of a Leyden jar that has just been discharg- 
ed. (Vs. St., IX, p. 473.) Pincus has also noticed the ozone odor in similar ex- 
periments with alcohol and oil (Argand) lamps, and with stearine candles. 

Doubtless, therefore, we are justified in making the generalization that in all 
cases of oxidation ozone is formed, and in many instances a portion of it diffuses 
into the atmosphere and escapes immediate combination. 



68 HOW CROPS FEED. 

themselves with this subject. The most recent investiga- 
tions of Daubeny, (Journal Ghem. /Soc, 1867, pp. 1-28,) 
lead to the conclusion that ozone is exhaled by plants, a 
conclusion previously adopted by Scoutetten, Poey, De 
Luca, and Kosmann, from less satisfactory data. Dau- 
beny found that air deprived of ozone by streaming 
through a solution of iodide of potassium, then made to 
pass the foliage of a plant confined in a glass bell and ex- 
posed to sunlight, acquired the power of blueing iodide- 
of-potassium-starch-paper, even when the latter was shield- 
ed from the light.* Cloez, however, obtained th,e contrary 
results in a series of experiments made by him in 1855, 
(Ann, de Chimie et de FAys., L, 326,) in which the oxy- 
gen, exhaled both from aquatic and land plants, contained 
in a large glass vessel, came into contact with iodide-of- 
potassium-starch-paper, situated in a narrow and blackened 
glass tube. Lawes, Gilbert, and Pugh, in their researches 
on the sources of the nitrogen of vegetation, (Phil. Trans.^ 
1861) examined the oxygen evolved from vegetable matter 
under the influence of strons: lig^ht, without findinof evidence 
of ozone. It is not impossible that ozone was really pro- 
duced in the circumstances of Cloez's experiments, but 
spent itself in some oxidizing action before it reached the 
test-paper. In Daubeny's experiments, however, the more 
rapid stream of air might have carried along over the test- 
paper enough ozone to give evidence of its presence. Al- 
though the question can hardly be considered settled, the 
evidence leads to the belief that vegetation itself is a 
source of ozone, and that this substance is exhaled, to- 
gether with ordinary oxygen, from the foliage, when acted 
on by sunlight. 

Ozone in the Atmosphere. — Atmospheric electricity, 
slow oxidation, and combustion, are obvious means of im- 
pregnating the atmosphere more or less with ozone. If 



* Light alone blues this paper after a time in absence of ozone. 



ATMOSPHERIC AIR AS THE FOOD OP PLANTS. 69 

the oxygen exhaled by plants contains ozone, this sub- 
stance must be perpetually formed in the atmosphere over 
a large share of the earth's surface. 

The quantity present in the atmosphere at any one time 
must be very small, since, from its strong tendency to unite 
with and oxidize other substances, it shortly disappears, 
and under most circumstances cannot manifest its peculiar 
properties, except as it is continually reproduced. The 
ozone present in any part of the atmosphere at any given 
moment is then, not what has been formed, but what re- 
mains after oxidable matters have been oxidized. We find, 
accordingly, that atmospheric ozone is most abundant in 
winter; since then there not only occurs the greatest 
amount of electrical excitement * in the atmosphere, which 
produces ozone, but the earth is covered with snow, and 
thus the oxidable matters of its surface are prevented 
from consuming the active oxygen. 

In the atmosj^here of crowded cities, in the vicinity of 
manure heaps, and wherever considerable quantities of or- 
ganic matters pervade the air, as revealed by their odor, 
there we find little or no ozone. There, however, it may 
actually be produced in the largest quantity, though from 
the excess of matters which at once combine with it, it 
cannot become manifest. 

That the atmosphere ordinarily cannot contain more 
than the minutest quantities of ozone, is evident, if we 
accept the statement (of Schunbein ?) that it communicates 
its odor distinctly to a million times its weight of air. 
The attempts to estimate the ozone of the atmosphere give 
varying results, but indicate a proportion far less than 
sufiicient to be recognized by the odor, viz., not more than 
1 part of ozone in 13 to 65 million of air. (Zwenger, 
Pless, and Pierre.) 

These figures convey no just idea of the quantities of 

* The amount of electrical disturbance is not measured by the number and 
violeace of thunder-storms : these only indicate its intensity. 



70 HOW CROPS FEED. 

ozone actually produced in the atmosphere and consumed 
in it. or at tiie suriace of the soil. We have as yet indeed 
no satisfactory means of information on this point, but 
may safely conclude from the foregoing considerations that 
ozone performs an important part in the economy of 
nature. 

Relations of Ozone to Vegetable \utrition. — Of the 
direct intlucnce of atmospheric ozone on plants, nothing 
is certamly known. Theoretically it should be consumed 
by them in various processes of oxidation, and would have 
ultimately the same efiects that are produced by ordinary 
oxygen. 

Indirectly, ozone is of great significance in our theory 
of vegetable nutrition, inasmuch as it is the cause of chem- 
ical changes which are of the highest importance in main- 
taining the life of plants. Tins tact will appear in the 
section on Xitric Acid, which follows. 



COMPOUNDS OF NITROGEN AND OXYGEN IN THE ATMOS- 
PHERE. 

\itric Acid* XO^IT. — Under the more common name 
Aqua /ortis (strong water ^i this highly important sub- 
stance is to be found in every apothecary shop. It is, 
when pure, a colorless, usually a yellow liquid, whose 
most obvious properties are its sour, burning taste, and 
power of dissolving, or acting upon, many metals and other 
bodies. 

When pure, it is a half heavier than its own bulk of 
water, and emits pungent, suffocating vapors or fumes ; in 
this state it is rarely seen, being in general mixed or di- 
luted with more or less water ; when very dilute, it evolves 
no fumes, and is even pleasant to the taste. 

It has the properties of an acid in the most eminent de- 
gree; vegetable blue colors are reddened by it, and it 



ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 71 

unites with great avidity to all basic bodies, forming a 
long list of nitrates. 

It is volatile, and evaporates on exposure to air, though 
not so rapidly as water. 

Nitric acid has a strong affinity for water ; hence its 
vapors, when they escape into moist air, condense the 
moisture, making therewith a visible cloud or fume. For 
the same reason the commercial acid is always more or less 
dilute, it being difficult or costly to remove the water en- 
tirely. 

Nitric acid, as it occurs in commerce, is made by heat- 
ing together sulphuric acid and nitrate of soda, when 
nitric acid distils off, and sulphate of soda remains behind. 

Nitrate of Sulphuric JBlsulphate of Nitric 
soda. acid. soda. acid. 

N03Na + H^SO, = HNa SO^ + NO3 H 

Nitrate of soda is formed in nature, and exists in im- 
mense accumulations in the southern part of Peru, (see 
p. 25-2.) 

Anliydroiiisi rVitric Aoid, X0O5, is whf\t is commonh- under- 
stood as existing in combination witli bases in the nitrates. It is a 
crystallized body, but is not an acid until it unites -with tlie elements of 
water. 

Nitrate of Ammonia, NH3 N03n, or NH, NO3, may 

be easily prepared by adding to nitric acid, ammonia in 
slight excess, and evaporating the solution. The salt read- 
ily crystallizes in long, flexible needles, or as a fibrous 
mass. It gathers moisture from the air, and dissolves in 
about half its weight of water. 

If nitrate of ammonia be mixed with potash, soda, or 
lime, or with the carbonates of these bases, an exchange 
of acids and bases takes place, the result of which is ni- 
trate of potash, soda, or lime, on the one hand, and free 
ammonia or carbonate of ammonia on the other. 

1%'itroiis Oxide, N2O.— "When nitrate of ammonia is heated, it 



72 HOW CROPS FEED. 

melts, and gradually decomposes into water and nitrous oxide, or 
"laughing gas," as represented by the equation : — 
NH4 NO3 = 3 H2O + NaO 

Nitric acid and the nitrates act as powerful oxidizing 
agents, i. e., they readily yield up a portion or all their 
oxygen to substances having strong affinities for this ele- 
ment. If, for example, charcoal be warmed with strong 
nitric acid, it is rapidly acted npon and converted into 
carbonic acid. If thrown into melted nitrate of soda or 
saltpeter, it takes fire, and is violently burned to carbonic 
acid. Similarly, sulphur, phosphorus, and most of the 
metals, may be oxidized by this acid. 

When nitric acid oxidizes other substances, it itself loses 
oxygen and suffers reduction to compounds of nitrogen, 
containing less oxygen. Some of these compounds require 
notice. 

IVitric Oxide, NO. — ^When nitric acid somewhat diluted 
with water acts upon metallic copper, a gas is evolved, 
which, after washing with water, is colorless and permanent. 
It is nitric oxide. By exposure to air it unites with oxy- 
gen, and forms red, suffocating fumes of nitric peroxide, 
or, if the oxygen be not in excess, nitrous acid is formed. 

Nitric Peroxide, (hyponitric acid,) NO^, appears as a 
dark yellowish-red gas when strong nitric acid is j^oured 
upon copper or tin exposed to the air. It is procured in 
a state of purity by strongly heating nitrate of lead : by 
a cold approaching zero of Fahrenheit's thermometer, it 
may be condensed to a yellow liquid or even solid, 

Nitrous Acid, (anhydrous,) N^Og, is produced when 
nitric peroxide is mixed with water at a low temperature, 
nitric acid being formed at the same time. 

Nitric peroxide. Water. Nitric acid. ^'*^^''^ «^*'^> 
^ anhydrous. 

4 NO, + H,0 = 2 NHO3 4- N, O3 

It may be procured as a blue liquid, which boils at the 
freezing point of water. 



ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 73 

When nitric peroxide is put in contact with solutions 
of an alkali, there results a mixture of nitrate and nitrite 
of the alkali. 

Nitric Hydrate of Nitrate of Nitrite of -^ * 
peroxide. potash. potash. potash. rVater. 

2 NO, + 2HK0 = NKO3 4- NKO, -f- H, O 

Nitrite of Ammonia, NH^ NO, is known to the chem- 
ist as a white crystalline solid, very soluble in water. 
When its concentrated aqueous solution is gently heated, 
the salt is gradually resolved into water and nitrogen gas. 
This decomposition is represented by the following equa- 
tion : 

NH^NO, = 2H,0 + 2N 

This decomposition is, however, not complete. A por- 
tion of ammonia escapes in the vapors, and nitrous acid 
accumulates in the residual liquid. (Pettenkofer.) Addi- 
tion of a strong acid facilitates decomposition; an, alkali 
retards it. When a dilute solution, 1 : 500, is boiled, but 
a small portion of the salt is decomposed, and a part of it 
is found in the distillate. Yery dilute solutions, 1 : 100,000, 
may be boiled without suffering any alteration whatever. 
(Schoyen.) 

Schonbein and others have (erroneously ?) supposed that 
nitrite of ammonia is generated by the direct union of 
nitrogen and water. Nitrite of ammonia may exist in the 
atmosphere in minute quantity. 

Nitrites cf potash and soda may be procured by strongly 
heating the corresponding nitrates, whereby oxygen gas is 
expelled. 

The Mutual Convertibility of Nitrates and Nitrites is 

illustrated by various statements already made. There 
are, in fact, numerous substances which reduce nitrates to 
nitrites. According to Schonbein, {Jour. PraJct. Ch.^ 84, 
207,) this reducing effect is exercised by the albuminoids, 
by starch, glucose, and milk-sugar, but not by cane-sugar. 
4 



74 HOW CROPS FEED. 

It is also manifested by many metals, as zinc, iron, and 
lead, and by any mixture evolving liydrogen, as, for ex- 
ample, putrefying organic matter. On the other hand, 
ozone instantly oxidizes nitrites to nitrates. 

Eediiction of Nitrates and Nitrites to Ammonia. — 

Some of the substances which convert nitrates into nitrites 
may also by their prolonged action transform the latter 
into ammonia. When small fragments of zinc and iron 
mixed together are drenched with warm solution of caustic 
potash, hydrogen is copiously disengaged. If a nitrate be 
a;lded to the mixture, it is at once reduced, and ammonia 
escapes. If to a mixture of zinc or iron and dilute chlor- 
hydric acid, such as is employed in preparing hydrogen 
gas, nitric acid, or any nitrate or nitrite be added, the 
evolution of hydrogen ceases, or is checked, and ammonia 
is formed in the solution, whence it can be expelled by 
lime or potash. 

J^ltrlc acid. Hydrogen. Ammonia, Water. 

NO3H + 8H = NH3 + 3H,0 

The appearance of nitrous acid in this process is an in- 
termediate step of the reduction. 

Furtlier Reduction of Nitric and Nitrous Acids. — ^Tin- 
der certain conditions nitric acid and nitrous acid are still 
further deoxidized. Nesbit, who first employed the reduc- 
tion of nitric acid to ammonia by means of zinc and dilute 
chlorhydric acid as a means of determining the quantity 
of the former, mentions (Quart. Jour. Ghem. jSoc, 1847, 
p. 283,) that when the temperature of the liquid is allowed 
to rise somewhat, nitric oxide gas, NO, escapes. 

From weak nitric acid, zinc causes the evolution of ni- 
trous oxide gas, IST^O. 

As already mentioned, nitrate of ammonia, when heated 
to fusion, evolves nitrous oxide, X.,0. Emmet showed 
that by immersing a strip of zinc in the rnclted salt, nearly 
pure nitrogen gas is set free. 



AT.MOSPIIERIC AIR AS THE FOOD OF PLANTS. 75 

When nitric ncid is heated with lean flesh (fibrin), nitric 
oxide and nitrogen gases both appear. It is thus seen 
that by successive steps of deoxidation nitric acid may 
be gradually reduced to nitrous acid, ammonia, nitric oxide, 
nitrous oxide, and finally to nitrogen. 

Tests for Nitric and J^itroias Acids. — The fact tlicat 
tliesc substances often occur in extremely minute quantities renders it 
needful to employ very delicate tests for their recognition. 

Fricc^s Test. — Free nitrous acid decomposes iodide of potassium in the 
same manner as ozone, and hence gives a blue color, with a mixture of 
this salt and starch-paste. Any nitrite produces the same effect if to 
the mixture dilute sulphuric acid be added to liberate the nitrous acid. 
Pure nitric acid, if moderately dilute, and dilute solutions of nitrates 
mixed with dilute sulphuric acid, are without immediate clfect upon 
iodide-of-potassium-starch-paste. If the solution of a nitrate be min- 
gled with dilute sulphuric acid, and agitated for some time with zinc 
filings, reduction to nitrite occurs, and then addition of the starch-paste, 
etc., gives the blue coloration. According to Schonbein, this test, first 
proposed by Price, will detect nitrous acid when mixed with one-hund- 
red-thousand times its weight of water. It is of course only applicable 
in the absence of other oxidizing agents. 

Green Vitriol Test. — A very characteristic test for nitric and nitrous 
acids, and a delicate one, though less sensitive than that just describ- 
ed, is furnished by common green vitriol, or protosulpliate of iron. 
Nitric oxide, the red gas which is evolved from nitric acid or nitrates by 
mixing them with excess of stroiig sulphuric acid., and from nitrous acid 
or nitrites by addition of dilute sulphuric acid., gives with green vitriol a 
peculiar blackish-brown coloration. To test for minute quantities of 
nitrous acid, mix the solution Avith dilute sulphuric acid aud cautiously 
pour this liquid upon an equal bulk of cold saturated solutioii of green 
vitriol, so that the former liquid floats upon the latter without mingling 
much with it. On standing, the coloration will be perceived where the 
two liquids are in contact. 

Nitric acid is tested as follows: Mix the solution of nitrate with an 
equal volume of concentrated sulphuric acid; let the mixture cool, and 
pour upon it the solution of green vitriol. The coloration will appear 
between the two liquids. 

Formation of Nitros^cn Compounds in the Atmosphere. 

— a. From free nitrogen, by electrical ozone. Schonbein 
and Meissner have demonstrated that a discharge of elec- 
tricity through air in its ordinary state of dryness causes 
oxygen and nitrogen to unite, with the formation of nitric 
peroxide, N0„. Meissner has proved that not the elec- 



76 HOW CROPS FEED. 

tricity directly, but the ozone developed by it, accom- 
plishes this oxidation. It has long been known that nitric 
peroxide decomposes with water, yielding nitric and ni- 
trous acids thus : 

2 NO, + H,0 = NO3H + NO,H. 

It is further known that nitrous acid, both in the free 
state and in combination, is instantly oxidized to nitric 
acid by contact with ozone. 

Thas is explained the ancient observation, first made by 
Cavendish in 1784, that when electrical sparks are trans- 
mitted through moist air, confined over solution of potash, 
nitrate of potash is formed. (For information regarding 
this salt, see p. 252.) 

Until recently, it has been supposed that nitric acid is 
present in only those rains which accompany thunder- 
storms. 

It appears, however, from the analyses of both Way and 
Boussingault, that visible or audible electric discharges 
do not perceptibly influence the proportion of nitric acid 
in the air ; the rains accompanying thunder-storms not 
being always nor usually richer in this substance than 
others. 

Von Babo and Meissner have demonstrated that silent 
electrical discharges develop more ozone than flashes of 
lightning. Meissner has shown that the electric spark 
causes the copious formation of nitric peroxide in its im- 
mediate path by virtue of the heat it excites, which in- 
creases the energy of the ozone simultaneously produced, 
and causes it to expend itself at once in the oxidation of 
nitrooren. Boussinajault informs us that in some of the 
tropical regions of South America audible electrical dis- 
charges are continually taking place throughout the whole 
year. In our latitudes electrical disturbance is perpetu- 
ally occurring, but equalizes itself mostly by silent dis- 
charge. The ozone thus noiselessly developed, though 
operating at a lower temperature, and therefore more 



ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 77 

slowly than that which is produced by lightning, must 
really oxidize much more nitrogen to nitric acid than the 
latter, because its action never ceases. 

Formation of Mtrogen Compounds in the Atmosphere. 

— h. From free nitrogen (by ozone ?) in the processes of 
combustion and slow oxidation. 

At high temperatures. — Saussure first observed {Ann. 
de Chimle^ Ixxi, 282), that in the burning of a mixture of 
oxygen and hydrogen gases in the air, the resulting water 
contains ammonia. He had previously noticed that nitric 
acid and nitrous acid are formed in the same process. 

Kolbe {Ann. Chem. it. Pharm.^ cxix, 176) found that 
when a jet of burning hydrogen was passed into the neck 
of an open bottle containing oxygen, reddish-yellow va- 
pors of nitrous acid or nitric peroxide were copiously pro- 
duced on atmospheric air becoming mingled with the 
burning gases. 

Bence Jones {Phil. Trans.., 1851, ii, 399) discovered ni- 
tric (nitrous ?) acid in the water resulting from the burn- 
ing of alcohol, hydrogen, coal, wax, and purified coal-gas. 

By the use of the iodide-of-potassium-starch test (Price's 
test), Boettger {Jour, far PraJct. Ghem.^ Ixxxv, 396) and 
Schonbein (ibid., Ixxxiv, 215) have more recently confirm- 
ed the result of Jones, but because they could detect 
neither free acid nor free alkali by the ordinary test-pa- 
pers, they concluded that nitrous acid and ammonia are 
simultaneously formed, that, in fact, nitrite of ammonia 
is generated in all cases of rapid combustion. 

Meissner ( JJntersuchungen ilber den Sauerstoff, 1863, p. 
283) was unable to satisfy himself that either nitrous acid 
or ammonia is generated in combustion. 

Finally, Zabelin {Ann. Chem. ii. Ph.^ cxxx, 54) in a 
series of careful experiments, found that when alcohol, il- 
luminating gas, and hydrogen, burn in the air, nitrous acid 
and ammonia are very frequently, but not always, formed. 



7S HOW CROPS FEED. 

When the combustion is so perfect that the resulting wa- 
ter is colorless and pure, only nitrous acid is formed ; 
when, on the other hand, a trace of organic matters es- 
capes oxidation, less or no nitrous acid, but in its place 
ammonia, appears in the water, and this under circum- 
stances that preclude its absor[)tion from the atmosphere. 

Zabelin gives no proof that the combustibles he em- 
ployed were absolutely free from compounds of nitrogen, 
but otherwise, his experiments are not open to criticism. 

Meissner*s observations were indeed made under some- 
what different conditions ; but his negative results were 
not improbably arrived at simply because he employed a 
much less delicate test for nitrous acid than was used by 
Schonbein, Boettger, Jones, and Zabelin.* 

We must conclude, then, that nitrous acid and ammonia 
are usually formed from atmospheric nitrogen during rap- 
id combustion of hydrogen and compounds of hydrogen 
and carbon. The quantity of these bodies thus generated 
is, however, in general so extremely small as to require the 
most sensitive reagents for their detection. 

At low teinperatures. — Schonbein was the first to observe 
that nitric acid may be formed at moderately elevated or 
even ordinary temperatures. He obtained several grams 
of nitrate of potash by adding carbonate of potash to the 
liquid resulting from the slow oxidation of phosphorus in 
the preparation of ozone. 

More recently he believed to have discovered that ni- 
trogen compounds are formed by the simple evaporation 
of water. He heated a vessel (which was indifferently of 



* Meissner rejected Price's test in the belief that it cannot serve to distin<?uish 
nitrous acid from peroxide of hydrogen. Ho O2. He therefore made the liquid 
to he examined allvaline with a slight excess of potash, concentrated to small 
hulk and tested with dilute sulphuric acid and protosulphate of iron. {Unters. 
u, d. Sauersfqf, p, 233), Schonhein had found that iodide of potassium is decom- 
posed after a little time by concentrated solutions of peroxide of hydrogen, but is 
unaffected by this body when dilute, {Jour, fdr j)rakt. Cliem., Ixxxvi, p. 90). 
Zabelin agrees with Schonbein that Price's test is decisive between peroxide of 
hydrogen and nitrous acid. {Ann, Chem, u. Ph., cxxx, p. 58.) 



ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 79 

glass, porcelain, silver, etc.,) so that water would evapo- 
rate rapidly from its surfoce. The purest water was then 
dropped into the warm dish in small quantities at a time, 
each portion being allowed to evaporate away before the 
next was added. Over the vapor thus generated was held 
the mouth of a cold bottle until a portion of the vapor 
was condensed in the latter. 

The w^ater thus collected gave the reactions for nitrous 
acid and ammonia, sometimes quite intensely, again faint- 
ly, and sometimes not at all. 

By simj^ly exposing a piece of filter-paper for a suffi- 
cient time to the vapors arising from pure water heated 
to boiling, and pouring a few drops of acidified iodide-of- 
potassium-starch-paste upon it, the reaction of nitrous acid 
was obtained. When paper which had been impregnated 
with dilute solution of pure potash was hung in the va- 
pors that arose from water heated in an open dish to 100° 
F., it shortly acquired so much nitrite of potash as to re- 
act with the above named test. 

Lastly, nitrous acid and ammonia appeared when a 
sheet of filter-paper, or a piece of linen cloth, which had 
been moistened with the purest water, was allowed to dry 
at ordinary temperatures, in the open air or in a closed 
vessel. {Jour, far Prakt. Ghem.^ Ixvi, 131.) These ex- 
periments of Schonbein are open to criticism, and do uot 
furnish perfectly satisfactory evidence that nitrous acid 
and ammonia are generated under the circumstances men- 
tioned. Bohlig has objected that these bodies might be 
gathered from the atmosphere, where they certainly exist, 
though in extremely minute quantity. 

Zabelin, in the paper before referred to {An7i. Gh. PA., 
cxxx, p. 76), communicates some experimental results 
which, in the writer's opinion, serve to clear up the mat- 
ter satisfactorily. 

Zabelin ascertained in the first place that the atmos- 
pheric air contained too little ammonia to influence Ness- 



80 



HOW CROPS FEED. 



ler's test,* which is of extreme delicacy, and which he con- 
stantly employed in his investigations. 

Zabelin operated in closed vessels. The apparatus he 
used consisted of two glass flasks, a larger and a smaller 
one, which were closed by corks and fitted with glass 
tubes, so that a stream of air entering the larger vessel 
should bubble through water covering its bottom, and 
thence passing into the smaller flask should stream through 
Nessler's test. Next, he found that no ammonia and 
(by Price's test) but doubtful traces of nitrous acid could 
be detected in the purest water when distilled alone in 
this apparatus. 

Zabelin likewise showed that cellulose (clippings of filter- 
paper or shreds of linen) yielded no ammonia to Nessler's 
test when heated in a current of air at temperatures of 
120° to 160° F. 

Lastly, he found that when cellulose and pure water to- 
gether were exposed to a current of air at the tempera- 
tures just named, ammonia was at once indicated by 
Nessler's test. Nitrous acid, however, could be detected, 
if at all, in the minutest traces only. 

Views of Schonbein. — The reader should observe that 
Boettger and Schonbein, finding in the first instance by 
the exceedingly sensitive test with iodide of potassium 
and starch-paste, that nitrous acid was formed, when hy- 
drogen burned in the air, while the water thus generated 
wns neutral in its reaction with the vastly less sensitive 
litmus test-paper, concluded that the nitrous acid was 
united with some base in the form of a neutral salt. Af- 
terward, the detection of ammonia appeared to demon- 
strate the formation of nitrite of ammonia. 

We have already seen that nitrite of ammonia, by ex- 
posure to a moderate heat, is resolved into nitrogen and 
water. Schonbein assumed that under the conditions of 






* See p. 54. 



ATMOSPHERIC AIU AS THE FOOD OF PLANTS. 81 

his experiments nitrogen and water combine to form ni- 
trite of ammonia. 

2N + 2H,0 = NH3, NO^H 

This theory, supported by the authority of so distin- 
guished a philosopher, has been ahnost universally credit- 
ed.* It has, however, little to warrant it, even in the way 
of probability. If traces of nitrite of ammonia can be 
produced by the immediate combination of these excep- 
tionally abundant and universally diffused bodies at com- 
mon temperatures, or at the boiling point of water, or 
lastly in close proximity to the flames of burning gases, 
then it is simply inconceivable that a good share of the 
atmosphere should not speedily dissolve in the ocean, for 
the conditions of SchOnbein's experiments preyail at all 
times and at all j^laces, so far as these substances are con- 
cerned. 

The discovery of Zabelin that ammonia and nitrous acid 
do not always appear in equivalent quantities or even 
simultaneously, Avhile difficult to reconcile Avith Schon- 
bein's theory, in no wise conflicts with any of his facts. 
A quantity of free nitrous acid that admits of recognition 
by help of Price's test would not necessarily have any 
efiect on litmus or other test for free acids. There re- 
mains, then, no necessity of assuming the generation of ni- 
trite of ammonia, and the fact of the separate appearance 
of the elements of this salt demands another explanation. 

The Author's Opinion. — The writer is not able, perhaps, 
to offer a fully satisfactory explanation of the facts above 
adduced. He submits, however, some speculations which 
appear to him entirely warranted by the present aspects 
of the case, in the hope that some one with the time at 



* Zabelin was inclined to believe that his failure to detect nitrous acid in some 
of his experiments where organic matters intervened, was due to a power pos- 
sessed by these organic matters to mask or impair the delicacy of Price's test, 
as first noticed by Pettenkofer and since demonstrated by Schonbeia in case of 
urine. 

4* 



82 HOW CROPS FEED. 

command for experimental study, will establish or disprove 
them by suitable investigations. 

He believes, from the existing evidence, that free nitro- 
gen can, in no case, unite directly with water, but in the 
conditions of all the foregoing experiments, it enters com- 
bination by the action of ozone^ as Schonbein formerly 
maintained and was the first to suggest. 

We have already recounted the evidence that goes to 
show the formation of ozone in all cases of oxidation, both 
at high and low^ temperatures, p. 67. 

In Zabelin's experiments we may suppose that ozone 
was formed by the oxidation of the cellulose (linen and 
paper) he em^^loyed. In Schonbein's experiments, wliere 
paper or linen w^as not employed, the dust of the air may 
have supplied the organic matters. 

The first result of the oxidation of nitrogen is nitrous 
acid alone (at least Schonbein and Bohlig detected no ni- 
tric acid), w^ien the combustion is complete, as in case of 
hydrogen, or when organic matters are excluded from the 
experiment. Nitric acid is a product of the subsequent 
oxidation of nitrous acid. When organic matters exist in 
the product of combustion, as when alcohol burns in a 
heated apparatus yielding water having a yellowish color, 
it is probable that nitrous acid is formed, but is afterward 
reduced to ammonia, as has been already explained, p. 74. 

Zabelin, in the article before cited, refers to Schonbein 
as authority for the fact that various organic bodies, viz., 
all the vegetable and animal albuminoids, gelatine, and 
most of the carbohydrates, especially starch, glucose, and 
milk-sugar, reduce nitrites to ammonia^ and ultimately to 
nitrogen ; and although we have not been able to find such 
a statement in those of Schonbein's jDapers to which we 
have had access, it is entirely credible and in accordance 
with numerous analogies. 

If, as thus appears extremely probable, ozone is devel- 
oped in all cases of oxidation, both rapid and slow, then 



ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 83 

every flame and fire, every decaying plant and animal, 
the organic matters that exhale from the skin and luno-s 
of living animals, or from the foliage and flowers of plants, 
especially, perhaps, the volatile oils of cone-bearing trees, 
are, indirectly, means of converting a portion of free ni- 
trogen into nitrous and nitric acids, or ammonia. 

These topics will be recurred to in our discussion of 
Nitrification in the Soil, p. 254. 

Formation of Nitrogen Compounds in the Atmosphere. 
— c. From free nitrogen by ozone accompanying the oxy- 
gen exhaled from green foliage in sunlight. 

The evidence upon the question of the emission of ozone 
by plants, or of its formation in the vicinity of foliage, has 
been briefly presented on page 68. The j^resent state of 
investigation does not permit us to pronounce definitely 
upon this point. There are, however, some foots of agri- 
culture which, perhaps, find their best explanation by as- 
suming this evolution of ozone. 

It has long been known that certain crops are especially 
aided in their growth by nitrogenous fertilizers, while oth- 
ers are comparatively indifierent to them. Thus the cereal 
grains and grasses are most frequently benefited by appli- 
cations of nitrate of soda, Peruvian guano, dung of ani- 
mals, fish, flesh and blood manures, or other matters rich 
in nitrogen. On the other hand, clover and turnips flour- 
ish best, as a rule, when treated with phosphates and alka- 
line substances, nnd are not manured with animal fertiliz- 
ers so economically as the cereals. It has, in fact, become 
a rule of practice in some of the best farming districts of 
England, where systematic rotation of crops is followed, 
to apply nitrogenous manures to the cereals and phos- 
phates to turnips. Again, it is a fact, that whereas nitro- 
genous manures are often necessary to produce a good 
wheat crop, in which, at 30 bu. of grain and 2,600 lbs. of 
straw, there is contained 45 lbs. of nitrogen ; a crop of 
clover may be produced without nitrogenous manure, in 



84 HOW CROPS FEED. 

which would be taken from the field twice or thrice the 
above amount of nitrogen, although the period of growth 
of the two crops is about the same. Ulbricht found in 
his investigation of the clover plant (Vs. St., lY., p. 27) 
that the soil appears to have but little influence on the 
content of nitrogen of clover, or of its individual organs. 
These facts admit of another expression, viz. : Clover, 
though containing two or three times more nitrogen, and 
requiring correspondingly larger supplies of nitrates and 
ammonia than wheat, is able to supply itself much more 
easily than the latter crop. In parts of the Genesee wheat 
region, it is the custom to alternate clover with wheat, be- 
cause the decay of the clover stubble and roots admirably 
prepares the ground for the last-named crop. The same 
preparation might be had by the more expensive process 
of dressing with a highly nitrogenous manure, and it is 
scarcely to be doubted that it is the nitrogen gathered by 
the clover which insures the wheat crop that follows. It 
thus appears that the plant itself causes the formation in 
its neighborhood of assimilable compounds of nitrogen, 
and that some plants excel others in their power of accom- 
plishing this important result. 

On the supposition that ozone is emitted by plants, it is 
plain that those crops Avhich produce the largest mass of 
foliage develop it most abundantly. By the action of 
this ozone, the nitrogen that bathes the leaves is convert- 
ed into nitric acid, which, in its turn, is absorbed by the 
plant. The foliage of clover, cut green, and of root crops, 
maintains its activity until the time the crop is gathered ; 
the supply of nitrates thus keeps pace with the wants of 
the plant. In case of grain crops, the functions of the fo- 
liage decline as the seed begins to develop, and the plant's 
means of providing itself with assimilable nitrogen fail, 
although the need for it still exists. Furthermore, the 
clover cut for hay, leaves behind much more roots and 
stubble per acre than grain crops, and the clover stubble 



ATIIOSPHERIC AIR AS THE FOOD OF PLANTS. 85 

is twice as rich in nitrogen as the stubble of ripened grain. 
This is a result of the fact that the clover is cut when in 
active growth, while the grain is harvested after the roots, 
stems, and leaves, have been exhausted of their own juices 
to Ti-^^et the demands of the seed. 

Whatever may be the value of our explanations, the 
fact is not to be denied that the soil is enriched in nitrogen 
by the culture of large-leaved plants, which are harvested 
while in active growth, and leave a considerable propor- 
tion of roots, leaves, or stubble, on the field. On the other 
hand, the field is impoverished in nitrogen when grain 
crops are raised upon it. 

Formation of Nitric Acid from Ammonia. — Ammonia 
(carbonate of ammonia) under the influence of ozone is 
converted into nitrate of ammonia, (Baumert, Houzeau). 
The reaction is such that one-half of the ammonia is oxid- 
ized to nitric acid, which unites with the residue and Avith 
water, as illustrated by the equation : 

2NH3 + 40 = NH,, NO3 + H,0 

In this manner, nitrate of ammonia may originate in the 
atmosphere, since, as already shown, ammonia and ozone 
are both present there. 

Oxidation and Reduction in tlie Atmosplierc. — The 

fact that ammonia and organic matters on the one hand, 
and ozone, nitrous and nitric acids on the other, are pres- 
ent, and, perhaps, constantly present in the air, involves at 
first thought a contradiction, for these two classes of sub- 
stances are in a sense incompatible with each other. 
Organic matters, ammonia, and nitrous acid, are converted 
by ozone into nitric acid. On the contrary, certain or- 
ganic matters reduce ozone to ordinary oxygen, or destroy 
it altogether, and reduce nitric and nitrous acids to am- 
monia, or, perhaps, to free nitrogen. The truth is that 
the substances named are being perpetually composed and 
decomposed in the atmosphere, and at the surface of the 



86 HOW CKOPS FEED. 

soil. Here, or at one moment, oxidation j^revails; there, 
or at another moment, reduction preponderates. It is 
only as one or another of the results of this incessant ac- 
tion is withdrawn from the sphere of change, that we can 
give it permanence and identify it. The quantities we 
measure are but resultants of forces that oppose each oth- 
er. The idea of rest or permanence is as foreign to the 
chemistry of the atmosphere as to its visible phenomena. 

Nitric Acid in the Atmosphere. — The occurrence of ni- 
tric acid or nitrate of ammonia in the atmosphere has been 
abundantly demonstrated in late years (1854-6) by Cloez, 
Boussingault, De Luca, and Ivletzinsky, who found that 
when large volumes of air are made to bubble through 
solutions of potash, or to stream over fragments of brick 
or pumice which have been soaked in potash or carbonate 
of potash, these absorbents gradually acquire a small 
amount of nitric acid. In the experiments of Cloez and 
De Luca, the air was first washed of its ammonia by con- 
tact with sulphuric acid. Their results prove, therefore, 
that the nitric acid v\^as formed independently of ammonia, 
though it doubtless exists in the air in combination with 
this base. 

Proportion of Nitric Acid in Rain-water, etc. — In at- 
mospheric waters, nitric acid is found much more abund- 
antly than in the air itself, for the reason that a small bulk 
of rain, etc., washes an immense volume of air. 

Many observers, among the first, Liebig, have found ni- 
trates in rain-water, especially in the rain of thunder- 
storms. The investigations of Boussingault, made in 
1856-8, have amply confirmed Barral's observation that 
nitric acid (in combination) is almost invariably present in 
rain, dew, fog, hail, and snow. Boussingault, {Agronomie^ 
etc.^ II, 325) determined the quantity of nitric acid in 134 
rains, 31 snows, 8 dews, and 7 fogs. In only 16 instances 
out of these 180 was the amount of nitric acid too small 



ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 87 

to detect. The greatest proportion of nitric acid found in 
rain occurred in a slow-falling morning shower, (9th Octo- 
ber, 1857, at Liebfrauenberg), viz., 62 parts * in 10 million 
of water. In fog, on one occasion, (at Paris, 19th Dec, 
1857,) 101 parts to 10 million of water were observed. 

Knop found in rain-water, collected near Leipzig, in 
July, 18G2, 56 parts ; in rain that fell during a thunder- 
storm, 98 parts in 10 million of water. 

Boussingault found in rain an average of 2 parts, in 
snow of 4 parts, of nitric acid to 10 million of water. 

Mr. Way, whose determinations of ammonia in the at- 
mospheric waters collected by Lawes and Gilbert, at 
Rothamstead, during the whole of the years 1855-6, have 
already been noticed, (p. 63,) likewise estimated the nitric 
.acid in the same waters. He found the proportion of ni- 
tric acid to be, in 1855, 4 parts, in 1856 4:^ parts, to 10 
million of water. 

Bretschneider found at Ida-Marienhlitte, Prussia, for the 
year 1865-6 an average of 8| parts, for 1866-7 an average 
of 4^ parts, of nitric acid in 10 million of water. At Regen- 
walde, Prussia, the average in 1865-6 was 25 parts, in 
1866-7, 22 parts. At Proskau, tlie average in 1864-5 was 
31 parts. At Kuschen, the average for 1864-5 was 6 
parts; in 1865-6,7; in 1866-7, 8 parts. At Dahme, in 
1865-6, the average was 12 parts. At Insterburg, Pincus 
and Rollig obtained in 1864-5, an average of 12 parts ; in 
1865-6, an average of 16 parts of nitric acid in 10 million 
of water. The highest monthly average was 280 parts, 
at Lauersfort, July, 1864; and the lowest was nothing, 
April, 1865, at Ida-Marienhiitte. 

Quantity ©f Nitric Acid in Atmospheric Water.— The 
total quantity of nitric acid that could be collected in the 
rains, etc., at Rothamstead, amounted in 1855 to 2.98 lbs., 
and in 1856 to 2.80 lbs. per acre. 



* In all the quantitative statements here and elsewhere, anhydrous nitric acid. 
No O5, (0=16, formerly NO 5, 0=8) is to be understood. 



88 



HOW CEOPS FEED. 



This quantity was very irregularly distributed among the 
months. In 1855 the smallest amount was collected in 
January, the largest in October, the latter being nearly 
20 times as much as the former. In 1856 the largest 
quantity occurred in May, and the smallest in February, 
the former not quite six times as much as the latter. 

The following table gives the results of Mr. Way entire. 
{Jour. Boy. Ag. Soc. of Mig., XVII, pp. 144 and 620.) 

Amounts of Rain and of Ammonia, Nitric Acid, and total Nitrogen 
therein, collected at Rothamstead, Eng., in the years 1855-6— calculated per 
acre, according to Messrs. Lawes, Gilbert, and Way. 



January. . . 
February . 

March 

April 

May 

June 

July 

August — 
September 
October. .. 
November 
December. 

Total. . 



Quantity of Bain 
ill Imperial Gal- 
lons, (1 gal. =10 
lbs. water.) 



1855 



13.52.3 
22.473 
52.484 
9.281 
52.575 
41.295 

157.713 
59.622 
34.875 

124.466 
59.950 
39.075 



1856 



62.952 
30.586 
22.722 
59.083 
106.474 
43.253 
33.561 
59.859 
47.477 
65.03317592 
32.181 3021 
50.870 2438 



Ammonia 

in 

grains. 



1855 1856 



1244 
2a37 
4513 
1141 
4206 
5574 
9620 
4769 
3313 



5005 
4175 
2108 
8614 
18313 
4870 
2869 
4214 
5972 
3921 
2591 
4070 



Nitric 
acid in 
grains. 



1855 1856 



230 

944 
1102 

325 
1840 
3303 
2680 
3577 

732 



1561 
544 
806 
1063 
3024 
2046 
1191 
2125 
1756 



Total Ni- 
trogen in 
grains. 



1855 1856 



448012075 
1007 1371 
664 2035 



1084 
2169 
3995 
1024 
3939 
5447 
8615 
4870 
2917 
7414 
2749 
2180 



4526 
3579 
1945 
7369 
15863 
4540 
2670 
4021 
5373 
3767 
2489 
3352 



663.332 

gairs. 



mil's, libs. 



9.53 
lbs. 



2.98 2.80 6.63 
lbs. libs, i lbs. 



lbs. 



According to Pincus and Rollig, the atmospheric water 
brought down at Insterburg, in the year ending with 
March, 1865, 7.225 lbs. av. of nitric acid per English acre 
of surface. 

The quantity of nitrogen that fell as ammonia was 
3.628 lbs.; that collected in the form of nitric acid was 
1.876 lbs. The total nitrogen of the atmospheric waters 
per acre, for the year, was 5.5 lbs. The rain-fall was 
392.707 imperial gallons. 

Bretschneider found in the atmospheric waters gathered 
at Ida-Marienhiltte, in Silesia, during 12 months ending 
April 15th, 1866, 3| lbs. of nitric acid per acre of surface. 

In Bretschneider's investigation, the amount of nitrogen 



I 



ATMOSPHERIC AIR AS THE FOOD OF PLAXTS. 89 

brought down per acre in the form of ammonia was 9.93G 
lbs.; that in the form of nitric acid was 0.974 lbs. The 
total nitrogen contained in the rain, etc., was accordingly 
10.91, or, in round numbers, 11 lbs. avoirdupois. The rain- 
fall amounted to 488.309 imperial gallons, (Wilda's Cen- 
tmlhlatt, August, 1866.) 

Relation of Nitric Acid to Ammonia in the Atmos- 
pliere. — The foregoing results demonstrate that there is 
in the aggregate an excess of ammonia over the amount 
required to form nitrate with the nitric acid. (In nitrate 
of ammonia (NH^ ^^3)5 ^^^ ^^^^ ^^^^ base contain the 
same quantity of nitrogen.) We are hence justified in 
assuming that the acid in question commonly occurs as ni- 
trate of ammonia * in the atmosphere. 

At times, however, the nitric acid may preponderate. 
One instance is on record {Journal de JPharmacie^ -A.pr., 
1845) of the presence of free nitric acid in hail, which fell 
at Nismes, in June, 1842. This hail is said to have been 
percejDtibly sour to the taste. 

Cloez ( Compt. Hendus, Hi, 527) found traces of free 
nitric acid in air taken 3 feet above the ground, especially 
at the beginning and end of winter. 

The same must have been true in the cases already giv- 
en, in which exceptionally large quantities of nitric acid 
w^ere found, in the examinations made by Boussingault and 
the Prussian chemists. 

The nitrate of ammonia which exists in the atmosphere 
is doubtless held there in a state of mechanical suspension. 
It is dissolved in the falling rains, and when once brought 
to the surface of the soil, cannot again find its way into 
the air by volatilization, as carbonate of ammonia does, 
but is permanently removed from the atmosphere, and 



* In evaporating large quantities of rain-water to dryness, there are often found 
in the residue nitrates of lime and soda. In these cases the lime and soda come 
from dust suspended in the air. 



90 HOW CROPS FEED. 

until in some way chemically decomposeil, belongs to the 
soil or to the rivers and seas. 

Nitrous Acid in the AtmoKpheric Waters. — In most of the researches up- 
on the quantity of nitric acid in the atmosphere and meteoric waters, 
nitrous acid has not been specially regarded. Tlie tests which serve to 
detect nitric acid nearly all apply equally well to nitrous acid, and no 
discrimiuatiou has been made until recently. According to Schonbein 
and Boblig, nitrates are sometimes absent from rain-water, but nitrites 
never. They occur, however, in but minute proportion. Pincus and 
Rollig observed but traces of nitrous acid in the waters gathered at 
Insterburg. Reichardt found no weighable quantity of nitrous acid in 
a sample of hail, the water from which contained in 10 million parts, 33 
parts ammonia and 5)^ parts of nitric acid. It is evident, then, that 
nitrous acid, if produced to any extent in the atmosphere, does not re- 
main as such, but is chiefly oxidized to nitric acid. 

In anj'^ case our data are probably not incorrect in respect to the 
quantity of nitrogen existing in both the forms of nitrous and nitric 
acids, although the former compound has not been separately estimated. 
The methods employed for the estimation of nitric acid would, in gen- 
eral, include the nitrous acid, with the single error of bringing the latter 
into the reckoning as a part of the former. 

Nitric Acid as Food of Plants. — A multitude of obser- 
vations, both in the field and laboratory, demonstrate that 
nitrates greatly promote vegetable growth. The extensive 
use of nitrate of soda as a fertilizer, and the extraordinary 
fertility of the tropical regions of India, whose soil until 
lately furnished a large share of the nitrate of potash of 
commerce, attest the fact. Furthermore, in many cases, 
nitrates have been found abundantly in fertile soils of tem- 
perate climates. 

Experiments in artificial soil and in water-culture show 
not only that nitrates supply nitrogen to plants, but dem- 
onstrate beyond doubt that they alone are a sufficient 
source of this element, and that no other compound is so 
well adapted as nitric acid to furnish crops with nitrogen. 

Like ammonia-salts, the nitrates intensify the color, and 
increase, both absolutely and relatively, the quantity of 
nitrogen of the plant to which they are supplied. Their 
effect, when in excess, is also to favor the development of 
foliage at the expense of fruit. 



ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 91 

The nitrates do not appear to be absorbed by the plant 
to any great extent, except through the medium of the 
soil, since they cannot exist in the state of vapor and are 
brought down to the earth's surface by atmospheric waters. 

The full discussion of their nutritive effects must there- 
fore be deferred until the soil comes under notice. See 
Division II, p. 271. 

In § 10, p. 96, "Recapitulation of the Atmospheric 
Supplies of Food to Crops," the inadequacy of the at- 
mospheric nitrates will be noticed. 

§9. 

OTHER INGREDIENTS OF THE ATMOSPHERE; viz., 3rarsh Gas, 

Carbonic Oxide, mtrous Oxide, Hydrochloric Acid, Sulphurous Acid, 

Sulphydric Acid, Organic VajJors, Susjiended Solid Matters. 

There are several other gaseous bodies, some or all of which may oc- 
cur in the atmosphere in very minute quantities, but whose relations to 
vegetation, in the present state of our knowledge, appear to be of no 
practical moment. Since, however, they have been the subjects of in- 
vestigations or disquisition by agricultural chemists, they require to be 
briefly noticed. 

Marsli «as,* C H4.— This substance is a colorless and nearly 
odorless gas, which is formed almost invariably Avhen organic matters 
suffer decomposition in absence of oxygen. When a lump of coal or a 
billet of wood is strongly heated, portions of carbon and hydrogen 
unite to form this among several other substances. It is accordingly 
one of the ingredients of the gases whose combustion forms the flame 
of all fires and lamps. It is also produced in the decay of vegetable mat- 
ters, especially when they are immersed in water, as happens in sw:imps 
and stagnant ponds, and it often bubbles in large quantities from the 
bottom of ditches, when the mud is stirred. 

Pettenkofer and Volt have lately found that marsh gas is one of the 
gaseous products of the respiration or nutrition of animals. 

It is combustible at high temperatures, and burns with a yellowish, 
faintly luminous flame, to water and carbonic acid. It causes no ill ef- 
fects when breathed by animals if it be mixed with much air, though of 
itself it cannot support respiration. 



* Known also to chemists under the names of Light Carburetted Hydrogen, 
Hydride of Methyl and Methane. 



92 HOW CROPS FEED. 

The mode of its origin at once suggests its presence in the atmos- 
phere. Saussure observed that common air contains some gaseous com- 
pound or compounds of carbon, besides carbonic acid ; and Boussin- 
gault found in 1834 that the air at Paris contained a very small quantity 
(from two to eight-millionths) of liydrogen in some form of combina- 
tion besides water. These facts agree witli the supposition that marsh 
gas is a normal though minute and variable ingredient of the atmosphere. 

IS.ela,tions of Marsli Oas to Veg-etatioii.— Whether 
this gas is absorbed and assimilated by plants is a point on which we 
have at present no information. It might serve as a source both of car- 
bon and hydrogen ; but as these bodies are amply furnished by carbonic 
acid and water, and as it is by no means improbable that marsh gas it- 
self is actually converted into these substances by ozone, the question 
of its assimilation is one of little importance, and remains to be inves- 
tigated. 

Schultz (Johnston's Lectures on Ag. Chem., 2d Ed., 147) found on sev- 
eral occasions that the gas evolved from plants when exposed to the sun- 
light, instead of being pure oxj-gen, coutained a combustible admixture, 
so that it exploded violently on contact with a lighted taper. 

Tliis observation shows either that the healthy plants evolved a large 
amount of marsh gas, which forms with oxygen an explosive mixture 
(the fire-damp of coal-mines), or, as is most probable, that the vegetable 
matter entered into decomposition from too long continuance of the 
experiment. 

Boussingault has, however, recently found a minute proportion of 
marsh gasln the air exhaled from the leaves of plants that are exposed 
to sunlight tv7}e7i submerged i7i water. It does not appear when the leaves 
are surrounded by air, as the latest experiments of Boussingault, Cloez, 
and Corenwinder, agree in demonstrating. 

Carbonic Oxide, CO, is a gas destitute of color and odor. It 
burns in contact with air, with a flame that lias a fine blue color. The 
result of its combustion is carbonic acid, CO + O = COa- 

This gas is extremely poisonous to animals. Air containing a few 
per cent of it is unfit for respiration, and produces headache, insensi- 
bility, and death. 

Carbonic oxide may be obtained artificially by a variety of processes. 
If carbonic acid gas be made to stream slowly through a tube containing 
ignited charcoal, it is converted into carbonic oxide, COa -f C = 3 CO. 

Carbonic oxide is largely produced in all ordinary fires. The air which 
draws through a grate heaped with well-ignited coals, as it enters the 
bottom of the mass of fuel, loses a large portion of its oxygen, which 
there unites with carbon, forming carbonic acid. This gas is carried up 
into the heated coal, and there, where carbon is in excess, it takes up an- 
other proportion of this element, being converted into carbonic oxide. 
At the summit of the fire, where oxygen is abundant, the carbonic oxide 
burns again with its peculiar blue color, to carbonic acid, provided the 
heat be intense enough to inflame the gas, as is the case when the mass 



ATMOSPHEKIC AIR AS THE FOOD OF PLANTS. 93 

of fuel is tboroiigbly ignited. When, on tlie other hand, the fire is cov- 
ered Avith cold fuel, carbonic oxide escapes copiously into the atmos- 
phere. 

When crystallized oxalic acid is heated with oil of vitriol, it yields 
water to the latter, and falls into a mixture of carbonic acid and carbonic 
oxide. 

C2H2O4, 2H2O = COo + CO + 3HoO. 

' Carbonic oxide may, perhaps, be formed in small quantity in the de- 
cay of organic matters; though Corenwinder {Cornpt. Send., LX, 102) 
foiled to detect it in the rotting of manure. ^ 

Kelatioiis of Carl>OBaic Oxide to Vog eta tion.— Ac- 
cording to Saussure, while pea-plants languish and die when immersed 
in carbonic oxide, certain marsb plants {EpiloUum hirsuUim, Lythrum 
salicaria, and Polygonum persicaria) flourish as well in this gas as in com- 
mon air. Saussure's experiments with these plants lasted six weeks. 
Tiiere occurred an absorption of the gas and an evolution of oxygen. 
It is thus to be inferred that carbonic oxide may be a source of carbon 
to aquatic plants. 

Boussiugault {Compt. Reiid., LXI, 493) was unable to detect any action 
of the foliage of land plants upon carbonic oxide, either when the gas 
was pure or mixed with air. 

The carbonic oxide which Boussiugault found in 1863 in air exhaled 
from submerged leaves, proves to have been produced in the analyses, 
(from pyrogallate of potash,) and was not emitted by the leaves them- 
selves, as at first supposed, as both Cloez and Boussiugault have shown. 

I\itroiis Oxide, N2O.— This substance, the so-called laughing 
gas, is prepared from nitrate of ammonia by exposing that salt to a iieat 
somewhat higher than is necessary to fuse it. The salt decomposes into 
nitrous oxide and water. 

Nn4, NO3 = N2O + 3 IlaO. 

The gas is readily soluble in water, and has a sweetish odor and taste. 
When breathed, it at first produces a peculiar exhilarating eflfeet, which 
is followed by stupor and insensibility. 

This gas has never been demonstrated to exist in the atmosphere. In 
fact, our methods of analysis are incompetent to detect it, Avhen it is 
present in very minute quantity in a gaseous mixture. Knop is of the 
opinion that nitrous oxide may occur in the atmosphere, and has pub- 
lished an account of experiments {Journal fiir Frakt. Cheni., Vol.^ 59, 
p. 114) which, according to him, prove that it is absorbed by vegetation. 

Until nitrous oxide is shown to be accessible to plants, any further no- 
tice of it is unnecessary in a treatise of this kind. 

Hyclrocliloric Acid Gas, HCl, whose properties have been 
described in How Crops Grow, p. 118, is found in minute quantity in the 
air over salt marshes. It doubtless proceeds from the decomposition of 
the chloride of magnesium of sea- water. Spreugcl has surmised its ex- 



94 now CKOPS FEED. 

halation by sca-shorc plants. It is found in the air near soda-works, be- 
ing a product of the manufacture, and is destructive to vegetation. 

Seilpliaai'oiES Acid, SO2, and SwSpliytlric Acid, HS, (see 
H. C. G., p. 115,) may exist in the atmosphere as local emanations. In 
larf^e quantities, as when escaping from smelting works, roasting heaps, 
or manufactories, they often prove destructive to vegetation. In contact 
with air they quickly suffer oxidation to sulphuric acid, which, dissolv- 
ing in the water of rains, etc., becomes incorporated with the soil. 

Oj'S'sh^Sc Matters of whatever sort that escape as vapor into the 
atmosplicre and are there recognized by their odor, are rapidly oxidized 
and have no direct iuHuence upon vegetation, so fiir as is now known. 

Nnspciaded ^olid Matters isi tlie Atmosplftere.— 
The solid matters which are raised into the air by winds in the form of 
dust, and are often transported to great heights and distances, do not 
properly belong to the atmosphere, but to the soil. Their presence in 
tlie air explains the growth of certain plants {air-planU) when entirely 
disconnected from the soil, or of such as are found in pure sand or on 
the surface of rocks, incapable of performing the functions of the soil, 
except as dust accumulates upon them. 

Barral announced in 1863 {Jour. cVAg. pratique, p. 150) the discovery 
of phosphoric acid in rain-water. Robinet and Luea obtained the same 
result with water gathered near the surf\ice of the earth. Tiie latter 
found, however, that rain, collected at a height of 60 or more feet above 
the ground, was free from it. 

§ 10. 

RECAPITULATION OF THE ATMOSPHERIC SUPPLIES OF 
FOOD TO CROPS. 

Oxygen, whether requh*ed in the free state to effect 
chemical changes in the processes of organization, or in 
combination (in carbonic acid) to become an ingredient 
of the plant, is superabundantly supplied by the atmos- 
phere. 

€arl)OIl. — The carhonie acid of the atmosphere is a 
source of this element sufficient for the most rapid growth, 
as is abundantly demonstrated by the experiments in wa- 
ter culture, made by Nobbe and Siegert, and by Wolff, 
(IT. C. G., p. 170), in which oat and buckwheat plants 
were brought to more than the best agricultural develop- 



ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 



95 



ment, witli no other than the atmospheric supply of 
carbon. 

Hydrogen is adequately supplied to crops by water, 
which equally belongs to the Atmosphere and the Soil, 
although it enters the plant chiefly from the latter. 

Nitrogen exists in immense quantities in the atmosphere, 
and we may regard the latter as the primal source of this 
element to the organic world. In the atmosphere, how- 
e\^er, nitrogen exists for the most part in tlie free state, and 
is, as such, so we must believe from existing evidence, un- 
assimilable by crops. Its assimilable compounds, aimno- 
nia and nitric acid, occur in the atmosphere, but in pro- 
portions so minute, as to have no influence on vegetable 
growth directly appreciable by the methods of investiga- 
tion hitherto employed, unless they are collected and con- 
centrated by rain and dew. 

The subjoined Table gives a summary of the amount 
of nitrogen annually brought down in rain, snow, etc., 
upon an^acre of surface, according to the determinations 
hitherto made in England and Prussia. 

Amount of Assimilable Nitrogen annxtallt brought down et 
THE Atmospheric Waters. 



Locality. 



Rothamstead, Southern England 

Kuscheu, Province Posen, Prussia. 

Insterburg, near Koujgsberg, '^ 

Regenwalde, near Stettin, '' 

Ida-Marienhlitte, near Breslau, Silesia, || . 
Proskau, Silesia, [ 

Dahme, Province Brandenburg, 



Average. 



Tear. 



185.5* 

lS5(j* 

18()4-5t 

lS(1.5-6t 

lS04-5t 

18«!5-r)+ 

181)4-5+ 

lSi)5-6+ 

18(55* 

lS(i4-5t 

18(35= 



Nitrorjen 
l-)er Acre. 



G.63 lbs. 

8.31 '• 

1.8(i " 

2.50 '.' 

5.49 " 

6.81 " 

15.09 " 

10.38 " 

11.83 " 

20.91 " 

G.(J6 " 



^yaier 
per Acre. 

6,033,220 lbs. 

6,160.510 " 

2,680,086 " 

4,008,491 " 

,222,461 " 

5.383.478 " 

5,313,5(J2 " 

4,358,053 " 

4,8TT,545 " 

4,031,782 " 

3,868,646 " 



8.76 lbs. 



4.8(57.075 lbs. 



* From Jan. to Jan. t From Apr. to Apr. % From May to May. 

Direct Atmospheric Supply of Nitrogen Insufficient 
for Crops. — To estimate the adequacy of these atmos- 
pheric supplies of assimilable nitrogen, we may compare 
their amount with the quantity of nitrogen required in the 



96 now CROPS feed. 

eomposition of standard crops, and with the quantity con- 
tained in appropriate applications of nitrogenous fertil- 
izers. 

The average atmospheric supply of nutritive nitrogen 
in rain, etc., for 12 months, as above given, is much less 
than is necessary for ordinary crops. According to Dr. 
Anderson, the nitrogen in a crop of 28 bushels of wheat 
and 1 (long) ton 3 cwt. of straw, is 45^ lbs.; that in 2|- 
tons of meadow hay is 56 lbs. The nitrogen in a crop of 
clover hay of 2J (long) tons is no less than 108 lbs. Ob- 
viously, therefore, the atmospheric waters alone are in- 
capable of furnishing crops with the quantity of nitrogen 
they require. 

On the other hand, the atmospheric supply of nitrogen 
by rain, etc., is not inconsiderable, compared with the 
amount of nitro seen, which often forms an effective nianur- 
ing. Peruvian guano and nitrate of soda (Chili saltpeter) 
each contain about 15 per cent of nitrogen. The nitrogen 
of rain, estimated by the average above given, viz., 8f lbs., 
corresponds to 58 lbs. of these fertilizers. 200 lbs. of gua- 
no is for most field purposes a sufiicient application, and 
400 lbs. is a large manuring. In Great Britain, where ni- 
trate of soda is largely employed as a fertilizer, 112 lbs. 
of this substance is an ordinary dressing, which has been 
known to double the grass crop. 

We notice, however, that the amount of nitrogen sup- 
plied in the atmospheric waters is quite variable, as well 
for different localities as for different years, and for differ- 
ent periods of the year. At Kuschen, but 2-2|- lbs. were 
brouorht down asjainst 21 lbs. at Proskau. At Regenwalde 
the quantity was 15 lbs. in 1864-5, but the next year it 
was nearly 30 per cent less. In 1855, at Rothamstead, 
the greatest rain supply of nitrogen was in July, amount- 
ing to 1^ lbs., and in October nearly as much more was 
brought down; the least fell in January. In 1856 the 
largest amount, 2:^ lbs., fell in May; the next, 1 lb., in 



ATMOSPHERTC AIR AS THE FOOD OF PLANTS. 97 

April; and the least in March. At Ida-Marienhutte, 
Kuschen, and Regenwalde, hi 1865-6, nearly half the 
year's atmospheric nitrogen came down in summer ; but 
at Insterburg only 30 per cent fell in summer, while 40 
per cent came down in winter. 

The nitrogen that is brought down in winter, or in 
spring and autumn, when the fields are fallow, can be 
counted upon as of use to summer crops only so far as it 
remains in the soil in an assimilable form. It is well 
known that, in general, much more water evaporates from 
cultivated fields during the summer than falls upon them 
in the same period ; while in winter, the water that falls 
is in excess of that which evaporates. But how much of 
the winter's fall comes to supply the summer's evaporation, 
is an element of the calculation likely to be very variable, 
and not as yet determined in any instance. 

We conclude, then, that the direct atmospheric supply 
of assimilable nitrogen, though not unimportant, is insuf- 
ficient for crops. 

We must, therefore, look to the soil to supply a large 
share of this element, as well as to be the medium through 
which the assimilable atmospheric nitrogen chiefly enters 
the plant. 

The Other Ingredients of the Atmosphere, so far as 
we now know, are of no direct significance in the nutri- 
tion of agricultural plants. Indirectly, atmospheric ozone 
has an influence on the supplies of nitric acid, a point we 
shall recur to in a full discussion of the question of the 
Supplies of Nitrogen to Vegetation, in a subsequent 
chapter. 

§ 11. 

ASSIMILATION OF ATMOSPHERIC FOOD. 

Boussingault has suggested the very probable view that 

the first process of assimilation in the chlorophyll cells of 

the leaf, — where, under the solar influence, carbonic acid 

5 



98 HOW CROPS FEED. 

is absorbed and decomposed, and a nearly equal volume 
of oxygen is set free, — consists in the simultaneous deox- 
idation of carbonic acid and of water, whereby the former 
is reduced to carbonic oxide with loss of half its oxygen, 
and tlie latter to liydrogen with loss of all its oxygen, viz.: 

Carbonic , -nr * Carbonic , Hydro- , Oxy- 

.J + Water. = -^ + + 

acid oxide gen, gen. 

CO, + H,0 = CO + H, + O, 

In this reaction the oxygen set free is identical in bulk 
with the carbonic acid involved, and the residue retained 
in the plant, COH„, multiplied by 12, would give 12 
molecules of carbonic oxide and 24 atoms of hydrogen, 
which, chemically united, might constitute either glucoso 
or levulose, C,, H,^ Oj„, from which by elimination of 
HjO would result cane sugar and Arabic acid, while sepa- 
ration of 2II2O would give cellulose and the other mem- 
bers of its group. 

Whether the real chemical process be this or a different 
and more complicated one is at present a matter of vague 
probability. It is, notwithstanding, evident that this re- 
action expresses one of the principal results of the assim- 
ilation of Carbon and Hydrogen in the foliage of plants. 

§ 12. 

The following Tabular View may usefully servo the 

reader as a recapitulation of the chapter now finished. 

TABULAR VIEW OF THE RELATIONS OF THE ATMOSPHERIC 
INGREDIENTS TO THE LIFE OF PLANTS. 

Oxygen, by roots, flowers, ripening fruit, and by all 

growing;: parts. 
Carbonic Acid, by foliage and green parts, but only in 
the light. 

Absorbed J Ammonia, as carbonate, by foliage, probably at all times, 
by Plants. I Water, as liquid, through the roots. 

Nitrous Acid ] united to ammonia, and dissolved in wa- 
NiTRic Acid ) ter through the roots. 

?/°^^ ^ [uncertain. 
Marsh Gas ) 



THE ATMOSPHERE AS RELATED TO VEGETATION. 99 

Not absorbed j Nitrogen, 
by Plants. ( Water iu state of vapor. 

' Oxygen, "/ by foliage and green parts, but only in the 
Ozone? ) light. 
Marsh Gas in traces by aquatic plants ? 
Water, as vapor, from surface of plant at all times. 
, Carbonic Acid, from the growing parts at all times. 



Exhaled by 
Plants. 



CHAPTER II. 

THE ATMOSPHERE AS PHYSICALLY RELATED TO 
VEGETATION. 

§ 1' 
MANNER OF ABSORPTION OF GASEOUS FOOD BY THE PLANT. 

Closing here our study of tlie atmosphere considered as 
a source of the food of j^lants, we still need to remark 
somewhat upon the physical properties of gases in rela- 
tion to vegetable life ; so far, at least, as may give some 
idea of the means by which they gain access into the 
plant. 

Physical Constitution of the Atmosphere. — That the 

atmosphere is a mixture and not a chemical combination 
of its elements is a fact so evident as scarcely to require 
discussion. As we have seen, the proportions which sub- 
sist among its ingredients are not uniform, although they 
are ordinarily maintained within very narrow limits of va- 
riation. This is a sufficient proof that it is a mixture. 
The remarkable fact that very nearly the same relative 
quantities of Oxygen, Nitrogen, and Carbonic Acid, 
steadily exist in the atmosphere is due to the even balance 
which obtains between growth and decay, between life 
and death. The equally ren^iirkable fact that the gases 



100 HOW CROPS FEED. 

which compose the atmosphere are uniformly mixed to- 
gether without regard to their specific gravity, is but one 
result of a law of nature which we shall immediately 
notice. 

Diffusion of Gases. — Whenever two or more gases are 
brought into contact in a confined space, they instantly 
begin to intermingle, and continue so to do until, in a 
longer or shorter time, they are both equally diffused 
throughout the room they occupy. If two bottles, one 
filled with carbonic acid, the other with hydrogen, be con- 
nected by a tube no wider than a straw, and be placed so 
that the heavy carbonic acid is below the fifteen times 
lighter hydrogen, we shall find, after the lapse of a few 
hours, that the two gases have mingled somewhat, and in 
a few days they will be in a state of uniform mixture. On 
closer study of this phenomenon it has been discovered 
that gases diffuse with a rapidity proportioned to their 
lightness, the relative diffusibility being nearly in the in- 
verse ratio of the square roots of their specific gravities. 
By interposing a porous diaphragm between two gases of 
different densities, we may visibly exhibit the fact of their 
ready and unequal diffusion. For this purpose the dia- 
phragm must offer a partial resistance to the movement 
of the gases. Since the lighter gas j)asses more rapidly 
into the denser than the reverse, the space on one side of 
the membrane will be overfilled, while that on the other 
side will be partially emptied of gas. 

In the accompanying figure is represented a long glass 
tube, J, widened above into a funnel, and having cemented 
upon this an inverted cylindrical cup of unglazed porce- 
lain, a. The funnel rests in a round aperture made in the 
horizontal arm of the support, while the tube below dips 
beneath the surface of some water contained in the wine- 
glass. The porous cup, funnel, and tube, being occupied 
with common air, a glass bell, c, is filled with hydrogen 
gas and placed over the cup, as shown in the figure. In- 



THE ATMOSPHERE AS RELATED TO VEGETATION. lOl 



Btaiitly, bubbles begin to escape rapidly from the bottom 
of the tube through the water of the wine-glass, thus 
demonstrating that hydrogen passes into the cup faster 
than air can escape outwards 
through its pores. If the bell be 
removed, the cup is at once bathed 
again externally in common air, the 
light hydrogen floating instantly 
upwards, and now the water begins 
to rise in the tube in consequence of 
the return to the outer atmosphere 
of the hydrogen which before had 
diffused into the cup. 

It is the perpetual action of this 
diffusive tendency which maintains 
the atmosphere in a state of such 
uniform mixture that accurate ana- 
lyses of it give for oxygen and 
nitrogen almost identical figures, at 
all times of the day, at all seasons, 
all altitudes, and all situations, ex- 
cept near the central surface of 
large bodies of still water. Here, 
the fact that oxygen is more largely 
absorbed by water than nitrogen, 
diminishes by a minute amount the 
usual proportion of the former gas. 
If in a limited volume of a mixture of several gases a 
solid or liquid body be placed, which is capable of chemic- 
ally uniting with, or otherwise destroying the aeriform 
condition of one of the gases, it will at once absorb those 
particles of this gas which lie in its immediate vicinity, 
and thus disturb the uniformity of the remaining mixture. 
Uniformity at once tends to be restored by diffusion of a 
portion of the unabsorbed gas into the space that has been 
deprived of it, and thus the absorption and the diffusion 




Fig. 7. 



lt)2 



HOW CROPS PEED. 



keep pace with each other until all the absorbable air is 
rsmoved from the gaseous mixture, and condensed or fixed 
in the absorbent. 

In this manner, a portion of the atmosphere enclosed in 
a large glass vessel may be perfectly freed from watery 
vapor and carbonic acid by a small fragment of caustic 
potash. By standing over sulphuric acid, ammonia is 
taken from it ; a piece of phosphorus will in a few hours 
absorb all its oxygen, and an ignited mass of the rare 
metal titanium will remove its nitrogen. 

Osmose of Oases* — By this expression is understood the 
passage of gaseous bodies through membranes whose 
pores are too small to he discoverable by optical means^ 
such as the imperforate wall of the vegetable cell, the 
green cuticle of the plant where not interrupted by stomata, 
vegetable parchment, India rubber, and animal membranes, 
like bladder and similar visceral integuments. 

If a bottle filled with air have a thin sheet of India 
rubber, or a piece of moist bladder tied over its mouth 
and then be placed within a bell of hydrogen, evidence is 
at once had that gases penetrate the membrane, for it 
swells outwards, and may even burst by the pressure of 
the hydrogen that rapidly accumulates in the bottle. 

Gaseous Osmose is Diffusion Modified by tlie Influence 
of tlie Membrane* — The rapidity of osmose * is of course 
influenced by the thickness of the membrane, and the 
character of its pores. An adhesion between the mem- 
brane and the gases would necessarily increase their rate 
of penetration. In case the membrane should attract or 
have adhesion for one gas and not for another, complete 
separation of the two might be accomplished, and in pro- 
portion to the difference existing between two gases as re- 
gards adhesion for a given membrane, would be the de- 
gree to which such gases would be separated from each 



* The osmose of liquids is discussed in detail in "How Crops Grow," p. 354. 



THE ATMOSPHERE AS RELATED TO VEGETATION. 103 

Other in penetrating it. In case a membrane is moistened 
with water or other liquid, or by a solution of solid mat- 
ters, this would still further modify the result. 

Absorption of Gases by the Plant. — A few words will 
now suffice to apply these facts to the absorption of the 
nutritive gases by vegetation. The foliage of plants is 
freely permeable to gases, as has been set forth in " How 
Crops Grow," p. 289. The cells, or some portions of their, 
contents, absorb or condense carbonic acid and ammonia 
in a similar way, or at least with the same effect, as potash 
absorbs carbonic acid. As rapidly as these bodies are 
removed from the atmosphere surrounding or occupying 
the cells, they are re-supplied by diffusion from without ; 
so that although the quantities of gaseous plant-food con- 
tained in the air are, relatively considered, very small, 
they are by this grand natural law made to flow in con- 
tinuous streams toward every growing vegetable cell. 



DIVISION II. 

THE SOIL AS RELATED TO VEGETABLE 
PRODUCTION. 

CHAPTER I. 

INTRODUCTORY. 

For the Husbandman the Soil has this paramount un- 
portance, that it is the home of the roots of his crops and 
the exclusive theater of his labors in promoting their 
growth. Through it alone can he influence the amount 
of vegetable production, for the atmosphere, and the light 
and heat of the sun, are altogether beyond his control. 
Agriculture is the culture of the field. The value of the 
field lies in the quality of its soil. No study can have a 
grander material significance than the one which gives us 
a knowledge of the causes of fertility and barrenness, a 
knowledge of the means of economizing the one and over- 
coming the other, a knowledge of those natural laws 
which enable the farmer so to modify and manage his soil 
that all the deficiencies of the atmosphere or the vicissi- 
tudes of climate cannot deprive him of a suitable reward 
for his exertions. 

The atmosphere and all extra-terrestrial influences that 
affect the growth of plants are indeed in themselves 
beyond our control. We cannot modify them in kind or 
amount ; but we can influence their subserviency to our 
purposes through the medium of the soil by a proper un- 
derstanding of the characters of the latter. 
104 



INTRODTJCTORY. 105 

The General Functions of the Soil are of three kinds : 

1. The ashes of the plant whose nature and variations 
have been the subject of study in a former volume (H. 
C. G., pp. 111-201,) are exclusively derived from the soil. 
The latter is then concerned in the most direct manner 
with the nutrition of the plant. The substances which 
the plant acquires from the soil, so far as they are nutri- 
tive, may be collectively termed soil-food. 

2. The soil is a mechanical support to vegetation. The 
roots of the plant penetrate the pores of the soil in all 
directions side wise and downward from the point of their 
junction with the stem, and thus the latter is firmly 
braced to its upright position if that be natural to it, and 
in all cases is fixed to the source of its supplies of ash-in- 
gredients. 

3. By virtue of certain special (physical) qualities to be 
hereafter enumerated, the soil otherwise contributes to 
the well-being of the plant, tempering and storing the 
heat of the sun which is essential to the vital processes ; 
regulating the supplies of food, which, coming from itself 
or from external sources, form at any one time but a mi- 
nute fraction of its mass, and in various modes ensuring the 
co-operation of the conditions which must unite to produce 
the perfect plant. 

Variety of SoilSt — In nature we observe a vast variety 
of soils, which differ as much in their agricultural value 
as they do in their external appearance. We find large 
tracts of country covered with barren, drifting sands, on 
whose arid bosom only a few stunted pines or shriveled 
grasses find nourishment. Again there occur in the high- 
lands of Scotland and Bavaria, as well as in Prussia, and 
other temperate countries, enormous stretches of moor- 
land, bearing a nearly useless growth of heath or moss. 
In Southern Russia occurs a vast tract, two hundred mil- 
lions of acres in extent, of the tschornosem^ or black earth, 
5* 



106 HOW CROPS FEED. 

whicli is remarkable for its extraordinary and persistent 
fertility. The prairies of our own West, the bottom lands 
of the Scioto and other rivers of Ohio, are other examples 
of peculiar soils ; while on every farm, almost, may be 
found numerous gradations from clay to sand, from vege- 
table mould to gravel — gradations iu color, consistence, 
composition, and productiveness. 



CHAPTER II. 

ORIGIN AND FORMATION OF SOILS. 

Some consideration of the origin of soils is adapted to 
assist in understanding the reasons of their fertility. 
Geological studies give us reasons to believe that what is 
now soil was once, in chief part, solid rock. "We find in 
nearly all soils fragments of rock, recognizable as such by 
the eye, and by help of the microscope it is often easy to 
perceive that those portions of the soil which are impal- 
TDable to the feel are only minuter grains of the same rock. 

Rocks are aggregates or mixtures of certain minerals. 

Minerals, again, are chemical compounds of various ele- 
ments. 

We have therefore to consider : 

I. The Chemical Elements of Rocks. 

II. The Mineralogical Elements of Rocks. 

III. The Rocks themselves — their Kinds and Special 
Characters. 

IV. The Conversion of Rocks into Soils ; to which we 
may add : 

V. The Incorporation of Organic Matter with Soils. 



ORIGIN AND FORMATION OP SOILS. 107 

§ 1. 
THE CHEMICAL ELEMENTS OF ROCKS. 

The chemical elements of rocks, i. e., the constituents 
of the minerals which go to form rocks, include all the 
simple bodies known to science. Those, which, from their 
universal distribution and uses in agriculture, concern us 
immediately, are with one exception the same that have 
been noticed in a former volume as composing the ash of 
agricultural plants, viz.. Chlorine, Sulphur, Carbon, Silicon, 
Potassium, Sodium, Calcium, Magnesium, Iron, and Man- 
ganese. The description given of these elements and 
of their most important compounds in " How Crops Grow " 
Avill suffice. It is only needful to notice further a single 
element. 

Aluminum, Symbol Al., At. wt. 27.4, is a bluish silver- 
white metal, characterized by its remarkable lightness, 
having about the specific gravity of glass. It is now 
manufactured on a somewhat large scale in Paris and New- 
castle, and is employed in jewelry and ornamental work. 
It is prepared by a costly and complex process invented 
by Prof. Deville, of Paris, in 1854, which consists essen- 
tially in decomposing chloride of aluminum by metallic 
sodium, at a high heat, chloride of sodium (common 
salt) and metallic aluminum being produced, as shown by 
the equation, Al„^ Cl^ + 6 Na = 6 Na CI + 2 Al. 

By combining with oxygen, this metal yields but one 
oxide, which, like the highest oxide of iron, is a sesqui- 
oxide, viz.: 

Alumina, Al^ O3, Eq. 102.8. — When alum (double sul- 
phate of alumina and potash) is dissolved in water and 
ammonia added to the solution, a white gelatinous body 
separates, which is alumina combined with water, Al^ O3, 
3 H^O. By drying and strongly heating this hydrated 
alumina, a white powder remains, which is pure alumina. 



108 HOW CROPS FEED. 

In nature alumina is found in the form of emery. The 
sapphire and ruby are finely colored crystallized varieties 
of alumina, highly prized as gems. 

Hydrated alumina dissolves in acids, yielding a numer- 
ous class of salts, of which the sulphate and acetate are 
largely employed in dyeing and calico-printing. The sul- 
phate of alumina and potash is familiarly known under 
the name of alum, with which all are acquainted. Other 
compounds of alumina will be noticed presently. 

§2. 
MINERALOGICAL ELEMENTS OF ROCKS. 

The mineralogical elements or minerals * which compose 
rocks are very numerous. 

But little conception can be gained of the appearance 
of a mineral from a description alone. Actual inspection 
of the different varieties is necessary to enable one to rec- 
ognize them. The teacher should be provided with a 
collection to illustrate this subject. The true idea of their 
composition and use in forming rocks and soils may be 
gathered quite well, however, from the written page. For 
minute information concerning them, see Dana's Manual 
of Mineralogy. We shall notice the most important. 

Quartz. — Chemically speaking, this mineral is anhy- 
drous silica — silicic acid — a compound of silicon and ox- 
ygen, Si O^. It is one of the most abundant substances 
met with on the earth's surface. It is found in nature in 
six-sided crystals, and in irregular masses. It is usually 
colorless, or white, irregular in fracture, glassy in luster. 
It is very hard, readily scratching glass. (See H. C. G., 
p. 120.) 

Feldspar (field-spar) is, next to quartz, the most abund- 



* The word mineral, or mineral "species," here implies a definite chemical 
compound of natural occurrence. 



OEIGIN AND FORMATION OF SOILS. 109 

ant mineral. It is a compound of silica with alumina, 
and with one or more of the alkalies, and sometimes, vnth 
lime. Mineralogists distinguish several species of feld- 
spar according to their composition and crystallization. 
Feldspar is found in crystals or crystalline masses usually 
of a white, yellow, or flesh color, with a somewhat pearly 
luster on the smooth and level surfaces which it j^resents 
on fracture. It is scratched by, and does not scratch 
quartz. 

In the subjoined Table are given the mineralogical names 
and analyses of the principal varieties of feldspar. Ac- 
companying each analysis is its locality and the name of 
the analyst. 

Orthoclase. Albite, Oligoclase. Labradorite. 

Common or potash Sodafddspar. Soda-lime feldspar. Lime-soda 
feldspar. feldspar. 

New Rochelle, N. Y. Unionville, Pa. Haddam, Conn. Drummond, C. W. 



s. 


W 


. Johnson. 


M. C, Weld. 


G. J. Brush. 


T. S. Hunt. 


Silica, 




64.23 


66.86 


64.26 


54.70 


Alumina, 




20.42 


21.89 


21.90 


29.80 


Potash, 




12.4'? 




0.50 


0.33 


Soda, 




2.62 


8.78 


999 


2.44 


Lime, 




trace 


1.79 


2.15 


11.42 


Magnesia, 






0.48 







Oxide of iron. 


trace 






0.36 


Water, 




0.24 


0.48 


0.29 


0.40 



Mica is, perhaps, next to feldspar, the most abundant 
mineral. There are three principal varieties, viz.: Musco- 
vite, Phlogopite, and Biotite. They are silicates of alumi- 
na with potash, magnesia, lime, iron, and manganese. 

Mica bears the common name " isinglass." It readily 
splits into thin, elastic plates or leaves, has a brilliant 
luster, and a great variety of colors, — white, yellow, brown, 
green, and black. Muscovite, or muscovy glass, is some- 
times found in transparent sheets of great size, and is used 
in stove-doors and lamp-chimneys. It contains much 
alumina, and potash, or soda, and the black varieties oxide 
of iron. 

Phlogopite and Biotite contain a large percentage of 
magnesia, and often of oxide of iron. 



110 HOAV CROPS FEED. 

The following analyses represent these varieties. 

Muscovite. Phlogopite. Biotite. 



Litchfield, Mt.Leinster, Edwards, N. Burgess, Putnam Co., 

Conn. Ireland. N. Y. Canada. N. Y. Siberia. 
Smith & Brush. Haughton, W. J.Craw. T.S.Hnnt. Smith & Brush. H. Rose. 

Silica, 44. GO 44.64 40.30 40.97 39.62 40.00 

Alumina, 36.23 30.18 16.45 18.56 17.35 12.67 

Oxide of iron, 1.34 6.35 trace 5.40 19.03 

Oxifl«iof 0.63 

manganese. 

Magnesia, 0.37 0.72 29.55 25.80 23.85 15.70 

Lime, 0.50 

Potash, 6.20 12.40 7.23 8.26 8.95 5.61 

Soda, 4.10 4.94 1.08 1.01 

Water, 5.26 5.32 0.95 1.00 1.41 

Variable Composition of Minerals. — We notice in the 
micas that two analyses of the same species differ very 
considerably in the proportion, and to some extent in the 
kind, of their ingredients. Of the two muscovites the 
first contains 6° 1^ more of alumina than the second, while 
the second contains S^l^ more of oxide of iron than the 
first. Again, the second contains 12.4° 1^ of potash, but no 
soda and no lime, while the first reveals on analysis 4°| „ of 
soda and 0.5° |^ of lime, and contains correspondingly less 
potash. Similar differences are remarked in the other anal- 
yses, especially in those of Biotite. 

In fact, of the analyses of more than 50 micas which are 
given in mineralogical treatises, scarcely any two per- 
fectly agree. The same is true of many other minerals, 
especially of the amphiboles and pyroxenes presently to be 
noticed. In accordance with this variation in composition 
we notice extraordinary diversities in the color and ap- 
pearance of different specimens of the same mineral. 

This fact may appear to stand in contradiction to the 
statement above made that these minerals are definite 
combinations. In the infancy of mineralogy great per- 
plexity arose from the numerous varieties of minerals that 
were found — varieties that agreed together in certain char- 
acteristics, but widely differed in others. 



ORIGIN AND FORAIATION OP SOILS. Ill 

Isomorphism. — In 1830, Mitscheiiich, a Prussian phi- 
losopher, discovered that a number of the elementary 
bodies are capable oi replacing each other in combination^ 
from the fact of their natural crystalline form being identic- 
al ; they being, as he termed it, isomorphous^ or of liJce 
shape. Thus, magnesia, lime, protoxide of iron, protoxide 
of manganese, which are all protoxide-bases, form one 
group, each of whose members may take the place of the 
other. Alumina (Al^ O3) and oxide of iron (Fe^ O3) be- 
long to another group of sesquioxide-bases, one of which 
may replace the other; while in certain combinations 
silica and alumina replace each other as acids. 

These replacements, which may take place indefinitely 
within certain limits, thus may greatly affect the composi- 
tion without altering the constitution of a mineral. Of 
the mineral amphibole, for example, there are known a 
great number of varieties ; some pure white in color, con- 
taining, in addition to silica, magnesia and lime ; others 
pale green, a small portion of magnesia being replaced by 
protoxide of iron; others black, contaming alumina in 
place of a portion of silica, and with oxides of iron and 
manganese in large proportion. All these varieties of 
amphibole, however, admit of one expression of their 
constitution, for the amount of oxygen in the bases, no 
matter what they are, or what their proportions, bears a 
constant relation to the oxygen of the silica (and alumina) 
they contain, the ratio being 1 : 2. 

If the protoxides be grouped together under the gen- 
eral symbol MO (metallic protoxide,) the composition of 
the araphiboles may be expressed by the formula MO SiO^. 

In pyroxene the same replacements of protoxide-bases 
on the one hand, and of silica and alumina on the other, 
occur in extreme range. (See analyses, p. 112.) The gen- 
eral formula which includes all the varieties of pyroxene 
is the same as that of amphibole. The distinction of am- 
phibole from pyroxene is one of crystallization. 



112 



HOW CEOPS FEED. 



"We might give in the same style formulae for all the 
minerals noticed in these pages, but for our purposes this 
is unnecessary. 

Amphibole is an abundant mineral often met with in 
distinct crystals or crystalline and fibrous masses, varying 
in color from pure white or gray {tremoUte, asbestus), light 
green (acthiolite), grayish or brownish green {anthophyl- 
lite), to dark green arid black (hornblende), according as 
it contains more or less oxides of iron and manganese. 
It is a silicate of magnesia and lime, or of magnesia and 
protoxide of iron, with more or less alkalies. 





White. 


Gray. 


Asli-gray. 


Black. 


Leek-green. 


Gouverneur, 


Lanark, 


Cummington, 


Brevig, 


Waldheim, 




N. Y. 


Canada. 


Mass. 


Norway. 


Saxony. 


Rammelsberg, 


T. S. Hunt. 


Smith & Brash, 


, Plantamour. 


Knop. 


Silica, 


57.40 


55.30 


50.74 


46.57 


58.71 


Magnesia, 


24. GO 


22.50 


10.31 


5.88 


10.01 


Lime, 


13.89 


13.36 


trace 


5.91 


11.53 


Protoxide of 












iron. 


1.36 


6.30 


33.14 


24.38 


5.65 


Protoxide of 




trace 


1.77 


2.07 




manganese, 












Alumina, 


1.38 


0.40 


0.89 


3.41 


1.52 


Soda, 




0.80 


0.54 


7.79 


12.38 


Potash, 




0.25 


trace 


2.96 





Water, 


0.40 


0.30 


3.04 




0.50 


Pyroxene is of 


very common occurrence, and 


consider- 


ably resembles hornblende 


in colors and in composition. 




White. 


Gray- White. 


Green. 


Black. 


Black. 




Ottawa, 


Bathurst, 


Lake 


Orange Co., 


Wetterau, 




Canada. 


Canada. 


Champlain. 


N. Y. 






T. S. Hunt. 


T. S. Hunt. 


Seybert. Smith & Brush. 


Gmelin. 


Silica, 


54.50 


51.50 


50.38 


39.30 


56.80 


Magnesia, 


18.14 


17.69 


6.-88 


2.98 


5.05 


Lime, 


25.87 


23.80 


19.33 


10.39 


4.85 


Protoxide 


1.98 




20.40 


30.40 


12.06 


of iron, 












Sesquioxide 




0.35 










of iron, 












Protoxide of 






trace 


0.67 


3.72 


manganese, 












Alumina, 




6.15 


1.83 


9.78 


15.32 


Soda, 








1.66 


3.14 


Potash, 








2.48 


0.34 


Water, 


0.40 


1.10 




1.95 






ORIGIN AND FORMATION OF SOILS. 113 

Chlorite is a common mineral occurring in small scales 
or plates which are brittle. It is soft, usually exists in 
masses, rarely crystallized, and is very variable in color 
and composition, though in general it has a grayish or 
brownish-green color, and contains magnesia, alumina, and 
iron, united with silica. See analysis below. 

Leucite is an anhydrous silicate of alumina found 
chiefly in volcanic rocks. It exists in white, hard, 24-sid- 
ed crystals. It is interesting as being formed at a high 
heat in melted lava, and as being the first mineral in Avhich 
potash was discovered (by Klaproth, in 1797). See anal- 
ysis below. 

Kaolinite is a hydrous silicate of alumina, w^hich is 
produced by the slow decomposition of feldspar under the 
action of air and water at the usual temperature. Form- 
ed in this way, in a more or less impure state, it consti- 
tutes the mass of white porcelain clay or kaolin, which is 
largely used in making the finer kinds of pottery. It ap- 
pears in white or yellowish crystalline scales of a pearly 
luster, or as an amorphous translucent powder of extreme 
fineness. Ordinary clay is a still more impure kaolinite. 







Chlorite. 
Steele Mine, N. 


Leucite. 
C. Vesuvius, 


Kaolinite. 




Summit Hill, 


Chaudiere 








Eruption of 1857 


Pa. Falls, Canada. 






Genth. 


Kammelsberg. 


S, W. Johnson. 


T.S.Hunt. 


SiliCca, 




24.90 


57.24 


45.93 


46.05 


Alumina, 




21.77 


22.96 


39.81 


38.37 


Sesquioxide 


of iron, 4.60 








Protoxide of 


iron, 


24.21 








Protoxide of 


manganese, 1.15 








Magnesia, 




12.78 







0.63 


Lime, 






0.91 




0.61 


Soda, 






0.93 






Potash, 






18.61 






Water, 




10.59 




14.02 


14.00 



Talc is often found in pale-green, flexible, inelastic scales 
or leaves, but much more commonly in compact gray 
masses, and is then known as soapstone. It is very soft, 



114 HOW CROPS FEED. 

has a greasy feel, and in composition is a hydrous silicate 
of magnesia. See analysis. 

Serpentine is a tough but soft massive mineral, in color 
usually of some shade of green. It forms immense beds 
in New England, New York, Pennsylvania, etc. It is also 
a hydrous silicate of magnesia. See analysis. 

Chrysolite is a silicate of magnesia and iron, which 
is found abundantly in lavas and basaltic rocks. It is a 
hard, glassy mineral, usually of an olive or brown-green 
color. See analysis below. 





Talc. 


. Serpentine. 


Chkysohte. 




Bristol, Conn. 


New Haven, 


Conn. 


Bolton, Mass. 




Dr. Lummis. 


G. 


J. Bru 


sh. 


G. 


J. Brush. 


Silica, 


64.00 




44.05 






40.94 


Alumina, 













0.27 


Protoxide of iron, 


4.75 




2.53 






4.37 


Magnesia, 


27.47 




39.24 






50. S4 


Lime, 












1.20 


Water, 


4.30 




13.19 






3.28 



Zeolites* — Under this general name mineralogists are 
in the habit of including a number of minerals which have 
recently acquired considerable agricultural interest, since 
they represent certain compounds which we have strong 
reasons to believe are formed in and greatly influence the 
properties of soils. They are hydrous silicates of alum- 
ina or lime, and alkali, and are remarkable for the ease 
with which they undergo decomposition under the influ- 
ence of weak acids. We give here the names and compo- 
sition of the most common zeolites. Their special signif- 
icance will come under notice hereafter. We may add 
that while they all occur in white or red crystallizations, 
often of great beauty, they likewise exist in a state of 
division so minute that the eye cannot recognize them, 
and thus form a large share of certain rocks, Avhich, by 
their disintegration, give origin to very fertile soils 



ORIGIN AND FOKMATION OF SOILS. 115 

Analcime. Chabasite. Natrolite. Scolecite. Tiiomsonite. 
Lake Superior. Nova Scotia. Bercren Hill, Ghaut's Tun- Magnet 











N.J. 


nel, India, 


Cove, Ark. 




C. T. Jackson. 


Rammelsbei 


•g. Brush. 


P. Collier. 


Smith & Brash. 


Silica, 


53.40 




52.14 


47.31 


45.80 


36.85 


Alumina, 


22.40 




19.14 


26.77 


25.55 


20.42 


Potash, 






0.08 


0.35 


0.30 





Soda, 


8.52 




0.71 


15.44 


0.17 


, 3.91 


Lime, 


3.00 




7.8-1 


0.41 


13.97 


13.95 


Magnesia 














Sesquioxide 










1.55 


of iron, 














Water, 


9.70 




■ 19.19 


9.84 


14.28 


13.80 




Stilbite. 


ArOPHYLLITE. 


Pectolite. 


Laumontite. Leonhardite. 


Nova Scotia. 


Lake Superior. 


Bergen Hill. 


Phippsburgh, Me. Lake Sup'r. 


S. W. Johnson 


. J, 


, L. Smith. J, 


, D. Whitney. 


Dufrenoy. 


Barnes, 


Silica, 


57.63 




52.08 


55.06 


51.98 


55.01 . 


Alumina, 


16.17 






1.45 


21.12 


22.34 


Potash, 






4.93 









Soda, 


1.55 






8.89 






Lime, 


8.08 




25.30 


32.86 


11.71 


10.64 


Water, 


16.07 




15.92 


2.96 


15.05 


11.93 



Calcite^ or Carhonate of Lime^ CaO CO^, exists in na- 
ture in immense quantities as a mineral and rock. Mar- 
ble, chalk, coral, limestone in numberless varieties, consist 
of this substance in a greater or less state of purity. 

Magncsite, or Carbonate of Magnesia^ MgO C0„, oc- 
curs to a limited extent as a white massive or crystallized 
mineral, resembling carbonate of lime. 

Dolomite, CaO C0„ + MgO C0„, is a compound of car- 
bonate of lime with carbonate of magnesia in variable 
proportions. It is found as a crystallized mineral, and is 
a very common rock, many so-called marbles and lime- 
stones consisting of or containing this mineral. 

Gypsum, oxJIydrous Sulphate of Lime, CaO SO^ + H^O, 
is a mineral that is widely distributed and quite abundant 
in nature. When "boiled" to expel the water it is 
Plaster of Paris. 

Pyrites, or Bisulphide of Iron, Fe S^, a yellow shining 
mineral often found in cubic or octahedral crystals, and 
frequently mistaken for gold (hence called fool's gold), 



116 



HOW CROPS FEED. 



is of almost universal occurrence in small quantities. Some 
forms of it easily oxidize when exposed to air, and furnish 
the green-vitriol (sulphate of protoxide of iron) of com- 
merce. 

Apatite and Phosphorite* — These names are applied to 
the native phosphate of lime, which is usually combined 
with some chlorine and fluorine, and may besides contain 
other ingredients. Apatite exists in considerable quantity 
at Hammond and Gouverneur, in St. Lawrence Co., N. 
Y., in beautiful, transparent, green crystals ; at South 
Burgess, Canada, in green crystals and crystalline masses ; 
at Hurdstown, N". J., in yellow crystalline masses; at 
Krageroe, Norway, in opaque flesh-colored crystals. In 
minute quantity apatite is of nearly universal distribution. 
The following analyses exhibit the composition of the 
principal varieties. 

^ Krageroe, 

Norway. 
Voelcker. 
53.84 
41.25 
4.10 
1.23? 
0.29 
0.38 
0.17 
0.42 

Phosphorite is the usual designation of the non-crystal- 
line varieties. 

Apatite may be regarded as a mixture in indefinite 
proportions of two isomorphous compounds, chlor apatite 
vcndi fluorapatite, neither of which has yet been found pure 
in nature, though they have been produced artificially. 



Lime, 

Phosphoric acid. 
Chlorine, 
Fluorine,* 
Oxide of iron. 
Alumina, 
Potash and soda. 
Water, 



Hurdstown, 

New Jersey. 

J. D. Whitney. 

53.37 

42.23 

1.02 

? 
trace 



* Fluorine was not determined in these analyses. The figures given for this 
element are calculated (by Kammelsberg), and are probably not far from the truth. 



OEIGIN AND FORMATION OF SOILS. 117 

These substances are again compounds of phosphate of 
lime, 3 CaO ^fi^t with chloride of calcium, Ca Cl^, or 
fluoride of calcium, Ca Fl^, respectively. 

§3. 
KOCKS— THEIR KINDS AND CHARACTERS. 

The Rocks which form the solid (unbroken) mass of " 
the earth are sometimes formed from a single mineral, but 
usually contain several minerals in a state of more or less 
intimate mixture. 

We shall briefly notice those rocks which have the 
greatest agricultural importance, on account of their com- 
mon and wide-spread occurrence, and shall regard them 
principally from the point of view of their chemical com- 
position^ since this is chiefly the clue to their agricultural 
significance. Some consideration of the origin of rocks, 
as well as of their structure^ will also be of service. 

Igneous Rocks. — A share of the rocks accessible to 
our observation are plainly of igneous origin^ i. e., their 
existing form is the one they assumed on cooling down 
from a state of fusion by heat. Such are the lavas that 
flow from volcanic craters. 

Sedimentary Rocks. — ^Another share of the rocks are 
oi aqueous origin, i. e., their materials have been deposit- 
ed from water in the form of mud, sand, or gravel, the 
loose sediment having been afterwards cemented and con- 
solidated to rock. The rocks of aqueous origin are also 
termed sedimentary rocks. 

Metamorphic Rocks. — Still another share of the rocks 
have resulted from the alteration of aqueous sediments or 
sedimentary rocks by the efiect of heat. Without sufier- 
ing fusion, the original materials have been more or less 
converted into new combinations or new forms. Thus 
limestone has been converted into statuary marble, and 



118 



HOW CROPS FEED. 



clay into granite. These rocks, which are the result of 
the united action of heat and water, are termed meta- 
morphic (i. e., metamorphosed) rocks. 

One of the most obvious division of rocks is into Crys- 
talline and Fragmented. 

Crystalline Rocks are those whose constituents crystal- 
lized at the time the rock was formed. Here belong both 
the igneous and metamorphic rocks. These are often 
plainly crystalline to the eye, i. e., are composed of readily 
jjerceptible crystals or crystalline grains, like statuary 
marble or granite ; but they are also frequently made up 
of crystals so minute, that the latter are only to be recog- 
nized by tracing them into their coarser varieties (basalt 
and trap.) 

Fra^mental Rocks are the sedimentary rocks, formed 
by the cementing of the fragments of other older rocks 
existing as mud, sand, etc. 

The Cbtstalline Rocks may be divided into two 
great classes, viz., the sillcious and calcareous ; the first 
class containing silica, the latter, lime, as the predomina- 
ting ingredient. 

The silicious rocks fall into three parallel series, which 
have close relations to each other. 1. The Granitic series ; 
2. The Syenitic series; 3. The Talcose or Magnesian 
series. In all the silicious rocks quartz or feldspar is a 
prominent ingredient, and in most cases these two minerals 
are associated together. To the above are added, in the 
granitic series, mica y in the syenitic series, ampTiibole or 
pyroxene / and in the talcose series, talc^ chlorite^ or ser- 
pentine. The proportions of these minerals vary indef- 
initely. 

The Granitic Series 
consisting principally of Quartz^ Feldspar^ and Mica. 

Granite. — A hard, massive* rock, either finely or 



♦ Rocks are massive when they have no tendency to split ii.to slabs or plates. 



ORIGIN AND FORMATION OF SOILS. 119 

coarsely crystalline, of various shades of color, depending 
on the color and proportion of the constituent minerals, 
usually gray, grayish white, or flesh-red. In common 
granite the feldspar is orthoclase (potash-feldspar). A 
variety contains albite (soda-feldspar). Other kinds (less 
common) contain ollgodase and labradorite. 

Gneiss differs from granite in containing more mica, and 
in having a banded appearance and schistose * structure, 
due to the distribution of the mica in more or less parallel 
layers. It is cleavable along the planes of mica into 
coarse slabs. 

Mica-slate or 3Ilca-schist contains a still larger pro- 
portion of mica than gneiss ; it is perfectly schistose in 
structure, splitting easily into thin slabs, has a glistening 
appearance, and, in general, a grayish color. The coarse 
whetstones used for sharpening scythes, which are quar- 
ried in Connecticut and Rhode Island, consist of this min- 
eral. 

Argillite, Clay-slate, is a rock of fine texture, often 
not visibly crystalline, of dull or but slightly glistening 
surface, and having a great variety of colors, in general 
black, but not rarely red, green, or light gray. Argillite 
has usually a slaty cleavage, i. e., it splits into thin and 
smooth plates. It is extensively quarried in various local- 
ities for roofing, and writing-slates. Some of the finest 
varieties are used for whetstones or hones. 

Other Granitic Rocks. — Sometimes mica is absent ; in 
other cases the rock consists nearly or entirely o^ feldspar 
alone, or of quartz alone, or of mica and quartz. The 
rocks of this series often insensibly gradate into each oth- 
er, and by admixture of other minerals run into number- 
less varieties. 



* Schists or schistose rocks are those which have a tendency to break into 
Blabs or plates from the arrangement of some of the mineral ingredients in 
layers. 



120 how crops feed. 

The Stenitic Series 
consisting chiefly of Quartz^ Feldspar, and Amphibole. 

Syenite is granite, save that amphibole takes the place 
of mica. In appearance it is like granite ; its color is usu- 
ally dark gray. Syenite is a very tough and durable rock, 
often most valuable for building purposes. The famous 
Quincy granite of Massachusetts is a syenite. Syenitic 
Gneiss and Hornhlende Schist correspond to common 
Gneiss and Mica Schist, hornblende taking the place of 
mica. 

The Volcanic Series 
consisting of Feldspar, Amphibole or Pyroxene, and 
Zeolites. 

Diorite is a compact, tough, and heavy rock, common- 
ly greenish-black, brownish-black, or grayish-black in 
color. It contains amphibole, but no pyroxene, and is 
an ancient lava. 

Dolerite or Trap in the fine-grained varieties is scarcely 
to be distinguished from Diorite by the appearance, and is 
well exhibited in the Palisades of the Hudson and the 
East and West Rocks of New Haven. It contains pyrox- 
ene in place of amphibole. 

Basalt is like dolerite, but contains grains of chrysolite. 
The recent lavas of volcanic regions are commonly basaltic 
in composition, though very light and porous in texture. 

Porphyryt — Associated with basalt occur some feld- 
spathic lavas, of which porphyry is common. It consists 
of a compact base of feldspar, with disseminated crystals 
of feldspar usually lighter in color than the mass of the 
rock. 

Pumice is a vesicular rock, having nearly the composi- 
tion of feldspar. 

The Magnesiat^ Series 
consisting of Quartz, Feldspar and Talc, or Chlorite. 

Talcose Granite difiers from common granite in the 
substitution of talc for mica. Is a fragile and more easily 



ORIGIN AND FORMATION OF SOILS. 121 

decomposable rock than granite. It passes through talcose 
gneiss into 

Talcose Schist, which resembles mica-schist in colors 
and in facility of splitting into slabs, but has a less glis- 
tening luster and a soapy feel. 

Chloritic Schist resembles talcose schist, but has a less 
unctuous feel, and is generally of a dark green color. 

Related to the above are Steatite, or soapstone^ — nearly 
pure, granular talc; and Serpentine rock, consisting 
chiefly of serpentine. 

The above are the more common and wide-spread si- 
licious rocks. By the blending together of the different 
members of each series, and the related members of the 
different series, and by the introduction of other minerals 
into their composition, an almost endless variety of si- 
licious rocks has been produced. Turning now to the 

Crystalline Calcareous Rocks, we have 

Granular Limestone, consisting of a nearly pure car- 
bonate of lime, in more or less coarse grains or crystals, 
commonly white or gray in color, and having a glistening 
luster on a freshly broken surface. The finer kinds are 
employed as monumental marhle. 

Dolomite has all the appearance of granular limestone, 
but contains a large (variable) amount of carbonate of 
magnesia. 

The Fragmental or Sedimentary Rocks are as fol- 
lows : 

Conglomerates have resulted from the consolidation of 
rather coarse fragments of any kind of rock. According 
to the nature of the materials composing them, they may 
be granitic, syenitic, calcareous, basaltic, etc., etc, They 
pass into 

Sandstones, which consist of small fragments (sand), 
are generally silicious in character, and often are nearly 
6 



122 HOW CROPS FEED. 

pure quartz. The freestone of the Connecticut Valley is 
a granitic sandstone, containing fragments of feldspar 
and spangles of mica. 

Other varieties are calcareous, argillaceous {clayey), 
basaltic, etc., etc. 

Slfales are soft, slaty rocks of various colors, gray, green, 
red, blue, and black. They consist of compacted clay. 
When crystallized by metamorphic action, they constitute 
arglllite. 

Limestones of the sedimentary kind are soft, compact, 
nearly lusterless rocks of various colors, usually gray, 
blue, or black. They are sometimes nearly pure carbon- 
ate of lime, but usually contain other substances, and are 
often liighly impure. When containing much carbonate 
of magnesia they are termed magnesian limestones. They 
l^ass into sandstones through intermediate calciferous 
sand rocJcs, and into shales through argillaceovs lime- 
stones. These impure limestones furnish the hydraulic 
cements of commerce. 

§4. 
CONVERSION OF ROCKS INTO SOILS. 

Soils are broken and decomposed rocks. We find in 
nearly all soils fragments of rock, recognizable as such by 
the eye, and by help of the microscope it is often easy to 
perceive that those portions of the soil which are impalpa- 
ble to the feel chiefly consist of minuter grains of the same 
rock. 

Geology makes probable that the globe was once in a 
melted condition, and came to its present state through a 
process of cooling. By loss of heat its exterior surface 
solidified to a crust of solid rock, totally incapable of sup- 
porting the life of agricultural plants, being impenetrable 
to their roots, and destitute of all the other external char- 
acterist^ics of a soil. 



OEIGIN AND rOEMATION OF SOILS. 123 

The first step towards the formation of a soil must have 
been the pulverization of the rock. This has been accom- 
plished by a variety of agencies acting through long pe- 
riods of time. The causes which could produce such re- 
sults are indeed stupendous when contrasted Avith the 
narrow experience of a single human life, but are really 
trifling compared with the magnitude of the earth itself, 
for the soil forms upon the surface of our globe, whose di- 
ameter is nearly 8,000 miles, a thin coating of dust, meas- 
ured in its greatest accumulations not by miles, nor 
scarcely by rods, but by feet. 

The conversion of rocks to soils has been performed, 
1st, by Changes of Temperature j 2d, by Moving Water 
or Ice y 3d, by the Chemical Action of Water and Air ^ 
4th, by the Influence of Vegetable and Animal life, 

1. — Changes of Temperatuee. 

The continued cooling of the globe after it had become 
enveloped in a solid rock-crust must have been accom- 
panied by a contraction of its volume. One effect of this 
shrinkage would have been a subsidence of portions of 
the crust, and a wrinkling of other portions, thus produc- 
ing on the one hand sea-basins and valleys, and on the 
other mountain ranges. Another effect Avould have been 
the cracking of the crust itself as the result of its own 
contraction. 

The pressure caused by contraction or by mere Aveight 
of sui3erincumbent matter doubtless led to the production 
of the laminated structure of slaty rocks, which may be 
readily imitated in wax and clay by aid of an hydraulic 
press. Basaltic and trap rocks in cooling from fusion often 
acquire a tendency to separate into vertical columns, 
somewhat as moist starch splits into five or six-sided frag- 
ments, when dried. These columns are again transversely 
jointed. The Giant's Causeway of Ireland is an illustra- 
tion. These fractures and joints are, perhaps, the first oc- 
casion of the breaking down of the rocks. The fact that 



124 ' HOW CROPS FEED. 

many rocks consist of crystalline grains of distinct min- 
erals more or less intimately Mended, is a point of weak- 
/ ness in their structure. The grains of quartz, feldsj^ar, 
and mica, of a granite, when exj^osed to changes of tem- 
perature, must tend to separate from each other; because 
the extent to which they expand and contract by alterna- 
tions of heat and cold are not absolutely equal, and be- 
cause, as Senarmont has proved, the same crystal expands 
or contracts unequally in its different diameters. 

Action of Freezing Water. — It is, however, when wa- 
ter insinuates itself into the slight or even imperceptible 
rifts thus opened, and then freezes, that the process of dis- 
integration becomes more rapid and more vigorous. Wa- 
ter in the act of conversion into ice expands iV of its bulk, 
and the force thus exerted is sufficient to burst vessels of 
the strongest materials. In cold latitudes or altitudes this 
agency working through many years accomplishes stupen- 
dous results. 

The adventurous explorer in the higher Swiss Alps fre- 
quently sees or hears the fall of fragments of rock thus 
loosened from the peaks. 

Along the base of the vertical trap cliffs of IS'ew Haven 
and the Hudson River, lie immense masses of broken rock 
reaching to more than half the height of the bluffs them- 
selves, rent off by this means. The same cause operates 
in a less conspicuous but not less important way on the 
surface of the stone, loosening the minute grains, as in 
the above instances it rends off enormous blocks. A 
smooth, clean pebble of the very compact Jura limestone, 
of such kind, for example, as abound in the rivers of 
South Bavaria, if moistened with water and exposed over 
night to sharp frost, on thawing, is muddy with the de- 
tached particles. 

2. — Moving Water or Ice. 

Changes of temperature not only have created differ- 
ences of level in the earth's surface, but they cause a con- 



ORIGIN AND FORMATION OF SOILS. 125 

tinual transfer of water from lower to higher levels. The 
elevated lands are cooler than the valleys. In their re- 
gion occurs a continual condensation of vapor from the 
atmosphere, which is as continually supplied from the 
heated valleys. In the mountains, thus begin, as rills, the 
streams of water, which, gathering volume in their descent, 
unite below to vast rivers that flow unceasingly into the 
ocean. 

These streams score their channels into the firmest rocks. 
Each grain of loosened material, as carried downward by 
the current, cuts the rock along which it is dragged so 
long as it is in motion. 

The sides of the channel being undermined and loosen- 
ed by exposure to the frosts, fall into the stream. In time 
of floods, and . always, when the path of the river has a 
rapid descent, the mere momentum of the water acts pow- 
erfully upon any inequalities of surface that oppose its 
course, tearing away the rocky walls of its channel. The 
blocks and grains of stone, thus set in motion, grind each 
other to smaller fragments, and when the turbid waters 
clear themselves in a lake or estuary, there results a bed 
of gravel, sand, or soil. Two hundred and sixty years 
ago, the bed of the Sicilian river Simeto was obstructed by 
the flow across it of a stream of lava from Etna. Since 
that time the river, with but slight descent, has cut a chan- 
nel through this hard basalt from fifty to several hundred 
feet wide, and in some parts forty to fifty deep. 

But the action of water in pulverizing rock is not com- 
pleted when it reaches the sea. The oceans are in perpet- 
ual agitation from tides, wind-waves, and currents like 
the Gulf-stream, and work continual changes on their 
shores. 

Glaciers. — What happens from the rapid flow of water 
down the sides of mountain slopes below the frost-line is 
also true of the streams of ice which more slowly descend 
from the frozen summits. The glaciers appear like motion- 



13G MOAV CROPS FEED. 

less ice-fields, but they are frozen rivers, rising in perpet- 
ual snows and melting into water, after having reached 
half a mile or a mile below the limits of frost. -The snow 
that accumulates on the frozen peaks of high mountains, 
which are bathed by moist winds, descends the slopes by 
its own weight. The rate of descent is slow, — a few 
inches, or, at the most, a few feet, daily. The motion it- 
self is not continuous, but intermittent by a succession of 
pushes. In the gorges, where many smaller glaciers unite, 
the mass has often a depth of a mile or more. Under the 
pressure of accumulation the snow is compacted to ice. 
Mingled with the snows are masses of rock broken off 
the higher pinnacles by the weight of adhering ice, or 
loosened by alternate freezing and thawing, below the hne 
of perpetual frost. The rocks thus falling on the edge of 
a glacier become a part of the latter, and partake its mo- 
tion. When the moving mass bends over a convex sur- 
face, it cracks vertically to a great depth. . Into the cre- 
vasses thus formed blocks of stone fall to the bottom, and 
water melted from the surface in hot days flows down and 
finds a channel beneath the ice. The middle of the glacier 
moves most rapidly, the sides and bottom being retarded 
by friction. The ice is thus rubbed and rolled upon itself, 
and the stones imbedded in it crush and grind each other 
to smaller fragments and • to dust. The rocky bed of the 
glacier is broken, and ploughed by the stones frozen into 
its sides and bottom. The glacier thus moves until it 
descends so low that ice cannot exist, and gradually dis- 
solves into a torrent whose waters are always thick with 
mud, and whose course is strewn with worn blocks of 
stone (boulders) for many miles. 

The Rhone, which is chiefly fed from the glaciers of the 
Alps, transports such a volume of rock-dust that its muddy 
waters may be traced for six or seven miles after they 
have poured themselves into the Mediterranean. 

3. — Chemical Action of Water and Air. 



ORIGI]^ AND FORMATION OF SOILS. 127 

Water acts chemically upon rocks, or rather upon their 
constituent minerals, in two ways, viz., ly Combinatiori 
and Solution. 

Hydration. — By chemically uniting itself to the mineral 
or to some ingredient of the mineral, there is formed in 
many instances a new compound, which, by being softer 
and more bulky than the original substance, is the first 
step towards further change. Mica, feldspar, amphibole, 
and pyroxene, are minerals which have been artificially 
produced in the slags or linings of smelting furnaces, and 
thus formed they have been found totally destitute of wa- 
ter, as might be expected from the high temperature in 
which they originated. Yet these minerals as occurring 
in nature, even when broken out of blocks of apparently 
unaltered rock, and especially when they have been di- 
rectly exposed to the weather, often, if not always, con- 
tain a small amount of water, in chemical combination 
(water of hydration). 

Solution,— As a solvent, water exercises the most im- 
portant influence in disintegrating minerals. Apatite, 
when containing much chlorine, is gradually decomposed 
by treatment with water, chloride of calcium, which is 
very soluble, being separated from the nearly insoluble 
phosphate of lime. The minerals which compose silicious 
rocks are all acted on perceptibly by pure water. This is 
readily observed when the minerals are employed in the 
state of fine powder. If pulverized feldspar, amphibole, 
etc. are simply m'oistened with pure water, the latter at 
once dissolves a trace of alkali, as shown by its turning 
red litmus-paper blue. This solvent action is so slight 
upon a smooth mass of the mineral as hardly to be per- 
ceptible, because the action is limited by the extent of 
surface. Pulverization, which increases the surface enor- 
mously, increases the solvent effect in a similar proportion. 
A glass vessel may have water boiled in it for hours with- 
out' its luster being dimmed or its surface materially acted 



128 HOW CROPS FEED. 

upon, whereas the same glass * finely pulverized is attack- 
ed by water so readily as to give at once a solution alka- 
line to the taste. Messrs. W. B. and R. E. Rogers {Am. 
Jour. /See., V, 404, 1848) found that by continued digestion 
of pure water for a week, with powdered feldspar, horn- 
blende, chlorite, serpentine, and natrolite,f these minerals 
yielded to the solvent from 0.4 to 1 per cent of their 
weight. 

In nature we never deal with pure water, but with wa- 
ter holding in solution various matters, either derived 
from the air or from the soil. These substances modify, 
and in most cases enhance, the solvent power of water. 

Action of Carbonic Acid, — This gaseous substance is 
absorbed by or dissolved in all natural waters to a greater 
or less extent. At common temperatures and pressure 
water is capable of taking up its own bulk of the gas. 
At lower temperatures, and imder increased pressure, the 
quantity dissolved is much greater. Carbonated water, 
as we may designate this solution, has a liigh solvent 
power on the carbonates of lime, magnesia, protoxide of 
iron, and protoxide of manganese. The salts just named 
are as good as insoluble in pure water, but they exist in 
considerable quantities in most natural waters. The 
spring and well waters of limestone regions are hard on 
account of their content of carbonate of lime. Chalyb- 
eate waters are those which hold carbonate of iron in 
solution. TThen carbonated water comes in contact with 
silicious minerals, these are decomposed much more rapidly 
than by jnire water. The lime, magnesia, and iron they 
contain, are partially removed in the form of carbonates. 

Struve ex2:)osed powdered phonolite (a rock composed 
of feldspar and zeohtes) to water saturated with carbonic 



♦ Glass is a silicate of potash or soda, 
t Mesotype. 



ORIGIX AND FORMATION OF SOILS. 129 

acid under a pressure of 3 atmospheres, and obtained a 
solution of which a pound * contained : 

Carbonate of soda, 22.0 grains. 

Chloride of sodium, 2.0 " 

Sulj)hate of potash, 1.7 " 

" soda, 4.8 " 

Carbonate of lime, 4.5 " 

'' " magnesia, 1.1 " 

Silica, 0.5 " 

Phosohoric acid and manganese, traces 



Total, 37.1 grains. 

In various natural springs, water comes to the surface 
so charged with carbonic acid that the latter escapes 
copiously in bubbles. Such waters dissolve large quantities 
of mineral matters from the rocks through which they 
emerge. Examples are seen in the springs at Saratoga, 
N. Y. According to Prof Chandler, the *' Saratoga 
Spring," whose waters issue directly from the rock, con- 
tains in one gallon of 231 cubic inches : 

grains. 



Chloride of Sodium (common salt) 


398.361 


" " Potassium, 




9.698 


Bromide of Sodium, 




0.571 


Iodide of Sodium, 




0.126 


Sulpliate of Potash, 




5.400 


Carbonate of Lime, 




86.483 


" " Magnesia, 




41.050 


" " Soda, 




8.948 


" " Protoxide of 


iron. 


.879 


Silica, 




1.283 


Phosphate of lime, 




trace 



Solid matters, 553.799 " 

Carbonic acid gas, (407.647 cubic inches at 52° Fah.) 
Water, 58,317.110 »' 

The waters of ordinary springs and rivers, as well as 
those that fall upon the earth's surface as rain, are, indeed, 



* The Saxon pound contains T,680 Saxon grains. 

6* 



130 HOW CROPS FEED. 

by no means fully charged with carbonic acid, and their 
solvent effect is much less than that exerted by water sat- 
urated with this gas. 

The quantity (by volume) of carbonic acid in 10,000 
parts of rain-water has been observed as follows : Accord- 
ing to 

Locality. 

Lampadius, 8 Country near Freiberg, Saxony. 

Mulder, 20 City of Utrecht, Holland. 

Von Baumhauer, 40 to 90 " " " " 

Peligot, 5 ? 

The quantities found are variable, as might be expected, 
and we notice that the largest proportion above cited does 
not even amount to one per cent. 

In river and spring water the quantities are somewhat 
larger, but the carbonic acid exists chiefly in chemical com- 
bination as bicarbonates of lime, magnesia, etc. 

In the capillary water of soils containing much organic 
matters, more carbonic acid is dissolved. According to a 
single observation of De Saussure's, such water contains 
2''|g of the gas. In a subsequent paragraph, p. 221, is 
given the reason of the small content of carbonic acid in 
these waters. 

The weaker action of these dilute solutions, when con- 
tinued through long periods of time and extending over 
an immense surface, nevertheless accomplishes results of 
vast significance. 

Solutions of Alkali-Salts. — Rain-water, as we have 
already seen, contains a minute quantity of salts of am- 
monia (nitrate and bicarbonate). The water of springs 
and rivers acquires from the rocks and soil, salts of soda 
and potash, of lime and magnesia. These solutions, dilute 
though they are, greatly surpass pure water, or even car- 
bonated water, in their solvent and disintegrating action. 
Phosphate of lime, the earth of bones, is dissolved by 
pure water to an extent that is hardly appreciable ; in 



ORIGIN AND F0R:MATI0X OF SOILS. 131 

salts of ammonia and of soda, however, it is taken up in 
considerable quantity. Solution of nitrate of ammonia 
dissolves lime and magnesia and their carbonates with 
great ease. In general, up to a certain limit, a saline so- 
lution acquires increased solvent power by increase in the 
amount and number of dissolved matters. This import- 
ant fact is one to which we shall recur at another time. 

Action of Oxygen.— This element, the great mover of 
chemical changes, which is present so largely in the at- 
mosphere, has a strong tendency to unite with certain 
bodies which are almost universally distributed in the 
rocks. On turning to the analyses of minerals, p. 110, we 
notice in nearly every instance a quantity of protoxide of 
iron, or protoxide of manganese. The green, dark gray, 
or black minerals, as the micas, amphibole, pyroxene, 
chlorite, talc, and serpentine, invariably contain these prot- 
oxides in notable proportion. In the feldspars they exist, 
indeed, in very minute quantity, but are almost never en- 
tirely wanting. Sulphide of iron (iron pyrites), in many 
of its forms, is also disposed to oxidize its sulphur to sul- 
phuric acid, its iron to sesquioxide, and this mineral is 
widely distributed as an admixture in many rocks. In 
trap or basaltic rocks, as at Bergen Hill, metallic iron is 
said to occur in minute proportion,* and in a state of fine 
division. The oxidation of these substances materially 
hastens the disintegration of the rocks containing them, 
since the higher oxides of iron and of manganese occupy 
more space than the metals or lower oxides. This fact is 
well illustrated by the sulphate of protoxide of iron (cop- 
peras, or green-vitriol), which, on long keeping, exposed to 
the air, is converted from transparent, glassy, green crys- 
tals to a bulky, brown, opaque powder of sulphate of 
sesquioxide of iron. 

Weathering. — The conjoined influence of water, car- 

♦ This statement rests on the authority of Professor Henry Wurtz, of New York. 



132 HOW CROPS FEED. 

bonic acid, oxygen, and the salts held in solution by the 
atmospheric waters, is expressed by the word v:eathering. 
This term may likewise include the action of frost." 

When rocks weather, they are decomposed or dissolved, 
and new compounds, or new forms of the original mat- 
ter, result. The soil is a mixture of broken or pulverized 
rocks, with the products of their alteration by weathering. 

a. Weathering of Quartz Rock. — Quartz (silicic acid), 
as occurring nearly pure in quartzite, and in many sand- 
stones, or as a chief ingredient of all the granitic, horn- 
blendic, and many other rocks, is so exceedingly hard and 
insoluble, that the lifetime of a man is not sufficient for 
the direct observation of any change in it, when it is ex- 
posed to ordinary weathering. It is, in fact, the least 
destructible of the mineral elements of the globe. Never- 
theless, quartz, even when pure, is not absolutely insoluble, 
particularly in water containing alkali carbonates or sili- 
cates. In its less pure varieties, and especially when as- 
sociated with readily decomposable minerals, it is acted 
on more rapidly. The quartz of granitic rocks is usually 
roughened on the surface when it has long been exposed 
to the weather. 

h. The Feldspars weather much more easily than 
quartz, though there are great differences among them. 
The soda and lime feldspars decompose most readily, 
while the potash feldspars are often exceedingly durable. 
The decomposition results in completely breaking up the 
hard, glassy mineral. In its place there remains a white 
or yellowish mass, which is so soft as to admit of crush- 
ing between the fingers, and which, though usually, to the 
naked eye, opaque, and non-crystalline, is often seen, under 
a powerful magnifier, to contain numerous transparent crys- 
talline plates. The mass consists principally of the crys- 
talline mineral, ^ao/mz^e, a hydrated silicate of alumina, (the 
analysis of which has been given already, p. 113,) mixed 



OKiGiN a:n'd fokmatiox of soils. 133 

with hydrated silica, and often with grains of undecompos- 
ed mineral. If we compare the composition of pure pot- 
ash feldspar with that of kaolinite, assuming, what is 
probably true, that all the alumina of the former remains 
in the latter, we find what portions of the feldspar have 
been removed and washed away by the water, which, to- 
gether with carbonic acid, is the agent of this change. 

Feldspar. Kaolinite. Liberated. Added. 

Alumina 18.3 18.3 

Silica 64.8 23.0 41.8 

Potash 16.9 16.9 

Water 6.4 6.4 

100 47.7 5a7 6^ 

It thus appears that, in the complete conversion of 100 
parts of potash feldspar into kaolinite, there result 47.7 
parts of the latter, while 58.7° 1^ of the feldspar, viz : 
41.8" Iq of silica and 16.9° j^ of potash, are dissolved out. 

The potash, and, in case of other feldspars, soda, lime, 
and magnesia, are dissolved as carbonates. If much water 
has access during the decomposition, all the liberated silica 
is carried away.* It usually happens, however, that a por- 
tion of the silica is retained in the kaolin (perhaps in a 
manner similar to that in which bone charcoal retains the 
coloring matters of crude sugar). The same is true of a 
portion of the alkali, lime, and oxide of iron, which may 
have existed in the original feldspar. 

The formation of kaolin may be often observed in na- 
ture. In mines, excavated in feldspathic rocks, the fis- 
sures and cavities through which surface water finds its 
way downwards are often coated or filled with this sub- 
stance. 

c. Other Siiicious Minerals, as Leucite, (Topaz, Scapo- 
lite,) etc., yield kaolin by decomposition. It is probable 
that the micas, which decompose with difficulty, (phlogo- 

* We have seen (H. C. G., p. 121) that silica, when newly set free from combi- 
natioD, is, at first, freely soluble in water. 



134 HOW CROPS FEED. 

pite, perhaps, excepted,) and the amphiboles and pyrox- 
enes, which are often easily disintegrated, also yield 
kaolin ; but in the case of these latter minerals, the result- 
ing kaolinite is largely mixed with oxides and silicates of 
iron and manganese, so that its properties are modified, 
and identification is difficult. Other hydrated silicates of 
alumina, closely allied to kaolinite, appear to be formed in 
the decomposition of compound silicates. 

Ordinary Clays, as pipe-clay, blue-clay, brick-clay, etc., 
are mixtures of kaolinite, or of a similar hydrated silicate 
of alumina, with a variety of other substances, as free 
silica, oxides, and silicates of iron and manganese, carbon- 
ate of lime, and fragments or fine powder of undecom- 
posed minerals. Fresenius deduces from his analyses of 
several Nassau clays the existence in them of a compound 
having the symbol Al^ O3 3 SiO^+H^O, and the follow- 
ing composition J9e?' cent. 

Silica, 57.14 

Alumina, 31.72 
Water, 11.14 

100.00 

Other chemists have assumed the existence of hydrated 
silicates of alumina of still different composition in clays, 
but kaolinite is the only one which occurs in a pure state, 
as indicated by its crystallization, and the existence of 
the others is not perfectly established. (S. W. Johnson 
and J. M. Blake on Kaolinite^ etc.^ A?n. Jour. JSoi., May^ 
1867, pp. 351-362.) 

d. The Zeolites readily suffer change by weathering ; 
little is known, however, as to the details of their disinte- 
gration. Instead of yielding kaolinite, they appear to be 
transformed into other zeolites, or retain something of their 
original chemical constitution, although mechanically dis- 
integrated or dissolved. We shall see hereafter that there 



OEIGIN AND FOEMATIOX OF SOILS. 135 

is strong reason to assume the existence of compounds 
analogous to zeolites in every soil. 

e. Serpentine and Mai^nesian Silicates are generally 
slow of decomposition, and yield a meager soil. 

f. The Limestones, when pure and compact, are very 
durable : as they become broken, or when impure, they 
often yield rapidly to the weather, and impregnate the 
streams which flow over them with carbonate of lime. 

g. Argillite and Arj^illaceous Limestones, which have 

resulted from the solidification of clays, readily yield clay 
again, either by simple pulverization or by pulverization 
and weathering, according as they have sufiered more or 
less change by metamorphism. 

§5. 

INCORPORATION OF ORGANIC MATTER WITH THE SOIL AND 
ITS EFFECTS. 

Antiquity of Vegetation. — Geological observations lead 
to the conclusion that but small portions of the earth's 
surface-rocks were formed previous to the existence of 
vegetation. The enormous tracts of coal found in every 
quarter of the globe are but the residues of preadamite 
forests, while in the oldest stratified rocks the remains of 
plants (marine) are either most distinctly traced, or the 
abundance of animal forms warrants us in assuming^ the 
existence of vegetation previous to their deposition. 

Tlie Development of Vej^etation on a purely Mineral 
Soil. — The mode in which the original inorganic soil be- 
came more or less impregnated with organic matter may 
be illustrated by what has happened in recent years upon 
the streams of lava that have issued from volcanoes. The 
lava flows from the crater as red-hot molten rock, often in 
masses of such depth and extent as to require months to 
cool down to the ordinary temperature. For many years 



136 HOW CROPS FEED. 

the lava is incapable of bearing any vegetation save some 
almost microscopic forms. During these years the surface 
of the rock suffers gradual disintegration by the agencies 
of air and water, and so in time acquires the power to 
support some lichens that appear at first as mere stains 
upon its surface. These, by their decay, increase the 
film of soil from which they sprung. The growth of 
new generations of these plants is more and more vigor- 
ous, and other superior kinds take root among them. 
After another period of years, there has accumulated a 
tangible soil, supporting herbaceous plants and dwarf 
«hrubs. Henceforward the increase proceeds more rapid- 
ly ; shrubs gradually give place to trees, and in a century, 
•more or less, the once hard, barren rock has leathered to 
a soil fit for vineyards and gardens. 

Those lowest orders of plants, the lichens and mosses, 
which prepare the way for forests and for agricultural 
vegetation, are able to extract nourishment from the most 
various and the most insoluble rocks. They occur abund- 
antly on all our granitic and schistose rocks. Even on 
quartz they do not refuse to grow. The white quartz 
hills of Berkshire, Massachusetts, are covered on their 
moister northern slopes with large patches of a leathery 
lichen, which adheres so firmly to the rock that, on being 
forced off, particles of the stone itself are detached. Many 
of the old marbles of Greece are incrusted with oxalate 
of lime left by the decay of lichens which have grown 
upon their surface. 

Humus* — By the decay of successive generations of 
plants the soil gradually acquires a certain content of dead 
organic matter. The falling leaves, seeds and stems of 
vegetation do not in general waste from the surface as 
rapidly as they are renewed. In forests, pastures, prai- 
ries, and marshes, there accumulates on the surface a brown 
or black mass, termed humus ^ of which leaf-mold, swamp- 
muck, and peat are varieties, differing in appearance as in 



OEIGIX AND FOEMATIOl^ OF SOILS. 137 

the circumstances of their origin. In the depths of the 
soil similar matters are formed by the decay of roots and 
other subterranean parts of plants, or by the inversion of 
sod and stubble, as well as by manuring. 

Decay of Vegetation. — When a plant or any part of a 
plant dies, and remains exposed to air and moisture at the 
common temperatures, it undergoes a series of chemical 
and physical changes, which are largely due to an oxida- 
tion of portions of its carbon and hydrogen, and the 
formation of new organic compounds. Vegetable matter 
is considerably variable in composition, but in all cases 
chiefly consists of cellulose and starch, or bodies of simi- 
lar character, mixed with a small proportion of albuminous 
and mineral substances. By decay, the white or light- 
colored and tough tissues of plants become converted into 
brown or black friable substances, in which less or none 
of the organized structure of the fresh plant can be . 
traced. The bulk and weight of the decaying matter 
constantly decreases as the process continues. With full 
access of air and at suitable temperatures, the decay, 
which, from the first, is characterized by the production 
and escape of carbonic acid and water, proceeds without 
interruption, though more and more slowly, until nearly 
all the carbon and hydrogen of the vegetable matters are 
oxidized to the above-named products, and little more 
than the ashes of the plant remains. With limited access 
of air the process rapidly runs through a first stage of 
oxidation, when it becomes checked by the formation of 
substances which are themselves able, to a good degree, 
to resist further oxidation, especially under the circum- 
stances of their formation, and hence they accumulate in 
considerable quantities. This happens in the lower layers 
of fallen leaves in a dense forest, in compost and manure 
heaps, in the sod of a meadow or pasture, and especially 
in swamps and peat-bogs. 

The more dehcate, porous and Avatery the vegetable 



138 HOW CROPS FEED. 

matter, and the more soluble substances and albuminoids 
it contains, the more rapidly does it decay or humify. 

It has been shown by a chemical examination of what 
escapes in the form of gas, as well as of what remains as 
humus, that the carbon of wood oxidizes more slowly 
than its hydrogen, so that humus is relatively richer in 
carbon than the vegetable matters from which it origin- 
ates. With imperfect access of air, carbon and hydrogen 
are to some extent disengaged in union with each other, 
as marsh gas (CHJ. Carbonic oxide gas (CO) is proba- 
bly also produced in minute quantity. The nitrogen of 
the vegetable matter is to a considerable extent liberated 
in the free gaseous state ; a portion of it unites to hydro- 
gen, forming ammonia (NH3), which remains in the de- 
caying mass ; still another portion remains in the humus 
in combination, not as ammonia, but as an ingredient of 
the ill-defined acid bodies which constitute the bulk of 
humus ; finally, some of the nitrogen may be oxidized to 
nitric acid. 

Chemical Nature of Humus* — In a subsequent chapter, 
(p. 224,) the composition of humus will be explained at 
length. Here we may simply mention that, under the in- 
fluence of alkalies and ammonia, it yields one or more 
bodies having acid characters, called humic and ulmic 
(also geic) aci^s. Further, by oxidation it gives rise to 
crenic and apocrenic acids. The former are faintly acid 
in their properties ; the latter are more distinctly char- 
acterized acids. 

Influence of Uumus on the Minerals of the Soil.— 

a. Disintegration of the mineral matters of soils is aided 
by the presence of organic substances in a decaying state, in 
so far as the latter, from their hygroscopic quality, main- 
tain the surface of the soil in a constant state of moisture. 

h. Organic matters furnish copious supplies of carbonic 
acid, the action of which has already been considered 



ORIGIN AND FORMATION OF SOILS. 139 

(p. 128). Boussingault and Lewy {Memoires de Ghimie 
Agrlcole, etc., p. 869,) have analyzed the air contained in 
the pores of the soil, and, as was to be anticipated, found 
it vastly richer in carbonic acid than the ordinary atmos- 
phere. 

The following table exhibits the composition of the air 
in the soil compared with that of the air above the soil, 
as observed in their investigations. 

Carbonic acid in 10,000 
parts of air (by weight). 

Ordinary atmosphere 6 

Air from sandy subsoil of forest 38 

" " loamy " " " 124 

" " surface-soil " " 130 

*' " " " vineyard 146 

" " *' ." old asparagus bed 123 

" " " " " " newly manured. ' 233 

" " " " pasture 270 

" " " rich in humus 543 

" " " newly manured sandy field, 

during dry weather 333 

" " " newly manured sandy field, 

during wet weather 1413 

That this carbonic acid originates in large part by oxi- 
dation of organic matters is strikingly demonstrated by 
the increase in its quantity, resulting from the application 
of manure, and the supervention of warm, wet weather. 
It is obvious that the carbonic acid contained in the air 
of the soil, being from twenty to one hundred or more 
times more abundant, relatively, than in the common at- 
mosphere, must act in a correspondingly more rapid and 
energetic manner in accomplishing the solution and disin- 
tegration of mineral matters. 

c. The organic acids of the humus group probably aid 
in the disintegration of soil by direct action, though our 
knowledge is too imperfect to warrant a positive conclu- 
sion. The ulmic and humic acids themselves, indeed, do 
not, according to Mulder, exist in the free state in the 
soil, but their soluble salts of ammonia, potash or soda, 
have acid characters, in so far that they unite energetical- 



140 HOW CROPS FEED. 

ly with other bases, as lime, oxide of iron, etc. These 
alkali-salts, then, should attack the minerals of the soil in 
a manner similar to carbonic acid. The same is probably 
true of crenic and apocrenic acids. 

d. It scarcely requires mention that the ammonia salts 
and nitrates yielded by the decay of plants, as well as the 
organic acids, oxalic, tartaric, etc., or acid-salts, and the 
chlorides, sulphates, and phosphates they contain, act upon 
the surface soil where they accumulate in the manner al- 
ready described, and that vegetable (and animal) remains 
thus indirectly hasten the solution of mineral matters. 

Action of Living Plants on the Minerals of the Soil.— 

1. Moisture and Carbonic Acid. — The living vegetation 
of a forest or prairie is the means of perpetually bringing 
the most vigorous disintegrating agencies to bear upon 
the soil that sustains it. The shelter of the growing 
plants, not less than the hygroscopic humus left by their 
decay, maintains the surface in a state of saturation by 
moisture. The carbonic acid produced in living roots, 
and to some extent, at least, it is certain, excreted from 
them, adds its effect to that derived from other sources. 

2. Organic Acids withiii the Flant, — According to 
Zoller, ( Vs. jSt. Y. 45) the young roots of living plants 
(what plants, is not mentioned) contain an acid or acid- 
salt which so impregnates the tissues as to manifest a 
strong acid reaction with (give a red color to) blue litmus- 
paper, which is permanent, and therefore not due to car- 
bonic acid. This acidity, Zoller informs us, is most in- 
tense in the finest fibrils, and is exhibited when the roots 
are simply wrapped in the litmus-paper, without being at 
all (?) crushed or broken. The acid, whatever it may be, 
thus existing within the roots is absorbed by porous paper 
placed externally to them. 

Previous to these observations of Zoller, Salm Horst- 
mar (Jour. fur. Praht. Chem. XL. 304,) having found in the 
ashes of ground pine (Lycopodium complanatum)^ 38° I,, of 



ORIGIN AND FORMATION OF SOILS. 141 

alumina, while in the ashes of juniper, growing beside 
the Lycopodium, this substance was absent, examined 
the rootlets of both plants, and found that the former had 
an acid reaction, w^hile the latter did not affect litmus- 
paper. Salm Horstraar supposed that the alumina of 
the soil finds its way into the Lycopodium by means of 
this acid. Ritthausen has shown that the Lycopodmm 
contains malic acid, and since all the alumina of the j^lant 
may be extracted by water, it is j^robable that the acid 
reaction of the rootlets is due, in part at least, to the 
presence of acid malate of alumina. {Jour. fur. PraJct. 
Chem. LIII. 420.) 

At Liebig's suggestion, Zuller made the following ex- 
periments. A number of glass tubes were filled with 
water made slightly acid by some drops of hydrochloric 
acid, vinegar, citric acid, bitartrate of potash, etc. ; the 
open end of each tube was then closed by a piece of 
moistened bladder tied tightly over, and various salts, in- 
soluble in water, as phosphate of lime, phosphate of am- 
monia and magnesia, etc., were strewn on the bladder. 
After a short time it was found that the ingredients of 
these salts were contained in the liquid in contact with 
the under surface of the bladder, having been dissolved 
by the dilute acid present in the pores of the membrane, 
and absorbed through it. This is an ingenious illustra- 
tion of the mode in which the organic acids existing in 
the root-cells of plants may act directly upon the rock or 
soil external to them. By such action is doubtless to be 
explained the fact mentioned by Liebig in the following 
words : 

"We frequently find in meadows smooth limestones 
with their surfaces covered with a network of small fur- 
rows. When these stones are newly taken out of the 
ground, we find that each furrow corresponds to a rootlet, 
which appears as if it had eaten its way into the stone." 
(Modern Ag. p. 43.) 



142 HOW CROPS FEED. 

This direct action of the living plant is probably ex- 
erted by the lichens, which, as has been already stated, 
grow upon the smooth surface of the rock itself. Many 
of the lichens are known to contain oxalate of lime to the 
extent of half their weight (Braconnot). 

According to Goeppert, the hard, fine-grained rock of the 
Zobtenberg, a mountain of Silesia, is in all cases softened at 
its surface where covered with lichens (Acarospora smar- 
agdidciy Imhricaria olivaceci^ etc.), while the bare rock, 
closely adjacent, is so hard as to resist the knife. On the 
Schwalbenstein, near Glatz, in Silesia, at a height of 4,500 
feet, the granite is disintegrated under a covering of li- 
chens, the feldspar being converted into kaolin or washed 
away, only the grains of quartz and mica remaining unal- 
tered.* 



CHAPTER III. 

KINDS OF SOILS— THEIR DEFINITION AND CLASSIFI- 
CATION. 

§ 1- 

DISTINCTION OF SOILS BASED UPON THE MODE OF THEIR 
FORMATION OR DEPOSITION. 

The foregoing considerations of the origin of soils intro- 
duce us appropriately to the study of soils themselves. 
In the next place we may profitably recount those defini- 
tions and distinctions that serve to give a certain degree 
of precision to language, and enable us to discriminate in 
some measure the different kinds of soils, which offer 
great diversity in origin, composition, external characters, 



* See, also, p. 136. 



KINDS OF SOILS. 143 

and fertility. Unfortunately, while there are almost num- 
berless varieties of soil having numberless grades of pro- 
ductive power, we are very deficient in terms by which to 
express concisely even the fact of their difierences, not to 
mention our inability to define these differences with ac- 
curacy, or our ignorance of the precise nature of their 
peculiarities. 

As regards mode of formation or deposition, soils are 
distinguished into Sederitary and Transported. Tl^e lat- 
ter are subdivided into Drif% Alluvial^ and Colluvial 
soils. 

Sedentary Soils, or Soils in place, are those which have 
not been transported by geological agencies, but which 
remain where they were formed, covering or contiguous 
to the rock from whose disintegration they originated. 
Sedentary soils have usually little depth. An inspection 
of the rock underlying such soils often furnishes most 
valuable information regarding their composition and 
probable agricultural value ; because the still un weathered 
rock reveals to the practised eye the nature of the min- 
erals, and thus of the elements, composing it, while in the 
soil these may be indistinguishable. 

In New England and the region lying north of the Ohio 
and east of the Missouri rivers, soils in place are not 
abundant as compared with the entire area. Nevertheless 
they do occur in many small patches. Thus the red-sand- 
stone of the Connecticut Valley often crops out in that 
part of New England, and, being, in many localities, of a 
friable nature, has crumbled to soil, which now lies undis- 
turbed in its original position. So, too, at the base of trap- 
bluffs may be found trap-soils, still full of starp-angled 
fragments of the rock. 

Transported Soils^ (subdivided into drift, alluvial, and 
colluvial), are those which have been removed to a dis- 
tance from the rock-beds whence they originated, by the 



144 HOW CROPS FEED. 

action of moving ice (glaciers) or water (rivers), and de- 
posited as sediment in their present positions. 

Drift Soils (sometimes called diluvial) are characterized 
by the following particulars. They consist of fragments 
whose edges at least have been rounded by friction, if the 
fragments themselves' are not altogether destitute of 
angles. They are usually deposited without any stratifi- 
cation or separation of parts. The materials consist of 
soil proper, mingled with stones of all sizes, from sand- 
grains up to immense rock-masses of many tons in weight. 
This kind of soil is usually distinguished from all others 
by the rounded rocks or boulders (" hard heads ") it con- 
tains, which are promiscuously scattered through it. 

The " Drift " has undoubtedly been formed by moving 
ice in that period of the earth's history known to geolo- 
gists as the Glacial Epoch, a period when the present sur- 
face of the country was covered to a great depth by fields 
of ice. 

In regions like Greenland and the Swiss Alps, which 
reach above the line of perpetual snow, drift is now ac- 
cumulating, perfectly similar in character to that of New 
England, or has been obviously produced by the melting 
of glaciers, which, in former geological ages and under 
a colder climate, were continuations on an immense scale 
of those now in existence. 

A large share of the northern portion of the country 
from the Arctic regions southward as far as latitude 39°, 
or nearly to the southern boundaries of Pennsylvania and 
to the Ohio River, including Canada, New England, Long 
Island, and the States west as far as Iowa, is more or less 
covered wiih drift. Comparison of the boulders with the 
undisturbed rocks of the regions about show that the 
materials of the drift have been moved southwards or 
southeastwards to a distance generj^ly of twenty to forty 
miles, but sometimes also of sixty or one hundred miles, 
from where they were detached from their original beds. 



KINDS OF SOILS. 



145 



The surface of the country when covered with drift is 
often or usually irregular and hilly, the hills themselves 
being conical heaps or long ridges of mingled sand, gravel, 
and Iboulders, the transported mass having often a great 
depth. These hills or ridges are parts of the vast trains 
of material left by the melting of preadamite glaciers or 
icebergs, and have their precise counterpart in the moraines 
of the Swiss Alps. Drift is accordmgly not confined to the 
valleys, but the northern slopes of mountains or hills, whose 
basis is unbroken rock, are strewn to the summit with it, 
and immense blocks of transported stone are seen upon 
the very tops of the Catskills and of the White and 
Green Mountains. 

Drift soils are for these reasons often made up of the 
most diverse materials, including all the kinds of rock and 
rock-dust that are to be found, or have existed for one or 
several scores of miles to the northward. Of these often 
only the harder granitic or silicious rocks remain in con- 
siderable fragments, the softer rocks having been com- 
pletely ground to powder. 

Towards the southern limit of the Drift Region the 
drift itself consists of fine materials which were carried 
on by the waters from the melting glaciers, while the 
heavier boulders were left further north. Here, too, may 
often be observed a partial stratification of the transported 
materials as the result of their deposition from moving 
water. The great belts of yellow and red sand that 
stretch across New Jersey on its southeastern face, and 
the sands of Long Island, are these finer portions of the 
drift. Farther to the north, many large areas of sand 
may, perhaps, prove on careful examination to mark the 
southern limit of some ancient local glacier. 

Alluvial Soils consist of worn and rounded materials 

which have been transported by the agency of running 

water (rivers and tides). Since small and light particles 

are more readily sustained in a current of water than 

7 



146 HOW CKOPS FEED* 

heavy masses, alluvium is always more or less stratified 
or arranged in distinct layers : stones or gravel at the 
bottom and nearest the source of movement, finer stones 
or finer gravel above and further down in the path of 
flow, sand and impalpable matters at the surface and at 
the point where the stream, before turbid from suspended 
rock-dust, finally clears itself by a broad level course and 
slow progress. 

Alluvial deposits have been formed in all periods of the 
earth's history. Water trickling gently down a granite 
slope carries forward the kaolinite arising from decompo- 
sition of feldspar, and the first hollow gradually fills up 
with a bed of clay. In valleys are thus deposited the 
gravel, sand, and rock-dust detached from the slopes of 
neighboring mountains. Lakes and gulfs become filled 
with silt brought into them by streams. Alluvium is 
found below as well as above the drift, and recent alluvium 
in the drift region is very often composed of drift mate- 
rials rearranged by water-currents. Alluvium often con- 
tains rounded fragments or disks of soft rocks, as lime- 
stones and slates, which are more rarely found in drift. 

Colluvial Soils, lastly, are those which, "while consisting 
in part of drift or alluvium, also contain sharp, angular 
fragments of the rock from which they mainly originated, 
thus demonstrating that they have not been transported 
to any great distance, or are made up of soils in place, 
more or less mingled with drift or alluvium. 

§2. 

DISTINCTIONS OF SOILS BASED UPON OBVIOUS OR EXTER- 
NAL CHARACTERS. 

The classification and nomenclature of soils customarily 
employed by agriculturists have chiefly arisen from con- 
sideration of the relative proportions of the principal 



KINDS OF SOILS. 147 

mechanical ingredients, or from other highly obvious 
qualities. 

The distinctions thus established, though very vague 
scientifically considered, are extremely useful for practical 
purposes, and the grounds upon which they rest deserve 
to be carefully reviewed for the purpose of appreciating 
their deficiencies and giving greater precision to the terms 
employed to define them. 

The farmer, speaking of soils, defines them as gravelly^ 
sandy ^ clayey^ loamy ^ calcareous^ peaty ^ ochreous^ etc. 

Mechanical Analysis of the Soil. — Before noticing 
these various distinctions in detail, we may appropriately 
study the methods which are employed for separating the 
mechanical ingredients of a soil. It is evident that the 
epithet sandy ^ for example, should not be applied to a soil 
unless sand be the predominating ingredient ; and in or- 
der to apply the term with strict correctness, as well as to 
know how a soil is constituted as regards its mechanical 
elements, it is necessary to isolate its parts and determine 
their relative quantity. 

Boulders, stones, and pebbles, are of little present or 
immediate value in the soil by way of feeding the plant. 
This function is performed by the finer and especially by 
the finest particles. Mechanical analysis serves therefore 
to compare together different soils, and to give useful in- 
dications of fertility. Simple inspection aided by the feel 
enables one to judge, perhaps, with sufficient accuracy for 
all ordinary practical purposes ; but in any serious attempt 
to define a soil precisely, for the purposes of science, its 
mechanical analysis must be made with care. 

Mechanical separation is effected by sifting and wash- 
ing. Sifting serves only to remove the stones and coarse 
sand. By placing the soil in a glass cylinder, adding wa- 
ter, and vigorously agitating for a few moments, then 
letting the whole come to rest, there remains suspended 
in the water a greater or less quantity of matter in a state 



148 HOW CROPS FEED. 

of extreme division. This fine matter is in many cases 
clay (kaolinite), or at least consists of substances resulting 
from the weathering of the rocks, and is not, or not chiefly, 
rock-dust. Between this impalpably fine matter and the 
grains of sand retained by a sieve, there exist numberless 
gradations of fineness in the particles. 

By conducting a slow stream of water through a tube 
to the bottom of a vessel, the fine particles of soil are 
carried off and may be received in a pan placed beneath. 
Increasing the rapidity of the current enables it to remove 
larger particles, and thus it is easy to separate the soil in- 
to a number of portions, each of which contains soil of a 
different fineness. 

Various attempts have been made to devise precise 
means of separating the materials of soils mechanically 
into a definite number of grades of fineness. 

This may be accomplished in good measure by washing, 
but constant and accurate results are of course only at- 
tained when the circumstances of the washing are uniform 
throughout. The method adopted by the Society of 
Agricultural Chemists of Germany is essentially the fol- 
lowing ( Yersuchs Stationen^ VI, 144) : 

The air-dry soil is gently rubbed on a tin-plate sieve 
with round holes three millimeters in diameter ; what passes 
is weighed as fine-earth. What remains on the sieve is 
washed with water, dried, weighed, and designated as 
gravel, pebbles, stones, as the case may be, the size of the 
stones, etc., being indicated by com23arison with the fist, 
with an egg^ a walnut, a hazelnut, a pea, etc. Of i\iQ fine- 
earth a portion (30 grams) is now boiled for an hour or more 
in water, so as to completely break down any lumps and 
separate adhering particles, and is then left at rest for 
some minutes, when it is transferred into the vessel 1 of 
the apparatus, fig. 8., after having poured off the turbid 
water with which it was boiled, into 2. This washing ap- 
paratus (invented by Nobel) consists of a reservoir, A^ 



KINDS OF SOILS. 



149 



made of sheet metal, capable of holding something more 
than 9 liters of water, and furnished at b with a stop-cock. 
By means of a tube of rubber it is joined to the series of 




Fig. 8. 

vessels, 1, 2, 3, and 4, which are connected to each other, 
as shown in the figure, the recurved neck of 2 fitting 
water-tight into the nozzle of 1 at a, etc. 

These vessels are made of glass, and together hold 4 
liters of water ; their relative volume is nearly 
1 : 8 : 27 : 64, or = 1^ : 2^ : 3^ : 4'. 

5 is a glass vessel of somewhat more than 5 liters, 
capacity. 

The distance between h and c is 2 feet. The cock, h, is 
opened, so that in 20 minutes exactly 9 liters of water 



150 HOW CROPS FEED. 

pass it. The apparatus being joined together, and the 
cock opened, the soil in 1 is agitated by the stream of wa- 
ter flowing through, and the finer portions are carried over 
into 2) 3) 4$ and 5. As a given amount of water requires 
eight times longer to pass through 2 than 1, its velocity 
of motion and buoyant power in the neck of 3 are corre- 
spondingly less. After the requisite amount of water has 
run from A, the cock is closed, the whole left to rest sev- 
eral hours, when the contents of the vessels are separately 
rinsed out into porcelain dishes, dried and weighed.* 

The contents of the several vessels are designated as 
follows :f 

1. Gravel, fragments of rock. 

2. Coarse sand. 

3. Fine sand. 

4. Finest or dust sand. 

5. Clayey substance or impalpable matter. 

In most inferior soils the (/ravel, the coarse sand, and 
the Jine sand, are angular fragments of quartz, feldspar, 
amphibole, pyroxene, and mica, or of rocks consisting of 
these minerals. It is only these harder and less easily 
decomposable minerals that can resist the pulverizing 
agencies through which a large share of our soils have 
passed. In the more fertile soils, formed from sedimen- 
tary limestones and slates, the fragments of these strati- 
fied rocks occur as flat pebbles and rounded grains. 

The finest or dust-sand, when viewed under the micro- 
scope, is found to be the same rocks in a higher state of 
pulverization. 



* See, also, Wolff's '■'■ Aitleitung zur Uniersuchung landwirtlischqftlich-wichtiger 
Stqfe,'' 1867, p. 5. 

t These names, applied by Wolff to the results of washing the sedentary soils 
of Wiirtemberg, do not always well apply to other soils. Thus Grouven, (3ter Salz- 
7nunder Bericht, p. 32), operating on the alluvial soils of North Germany, desig- 
nated the contents of the 4th funnel as "clay and loam," and those of the 5th 
vessel as " light clay and humus." Again, Schiine found {Bulletin, etc., de Moscou, 
p. 402) by treatment of a certain soil in NobcPs apparatus, 45 per cent of "coarse 
sand " remaining in the 2d funnel. The particles of this were for the most part 
Bmaller than 1-lOth millimeter (l-350th inch), which certainly is not coarse sand 1 



KINDS OF SOILS. 151 

What is designated as clayey 8uhstance^ or impalpable 
matter, is oftentimes largely made up of rock-dust, so fine 
that it is supported by water, Avhen the latter is in the 
gentlest motion. In what are properly termed clay-soils, 
the finest parts consist, however, chiefly of the hydrous 
silicate of alumina, already described, p. 113, under the 
mineralogical name of JcaoUnite, or of analogous com- 
pounds, mixed with gelatinous silica, oxides of iron, and 
carbonate of lime, as well as with finely divided quartz 
and other granitic minerals. So gradual is the transition 
from true kaolinite clay through its impurer sorts to mere 
impalpable rock-dust, in all that relates to sensible char- 
acters, as color, feel, adhesiveness, and plasticity, that the 
term clay is employed rather loosely in agriculture, being 
not infrequently given to soils that contain very little 
kaolinite or true clay, and thus implies the general physi- 
cal qualities that are usually typified by clay rather than 
the presence of any definite chemical compound, like 
kaolinite, in the soil. 

Many soils contain much carbonate of lime in an im- 
palpable form, this substance having been derived from 
lime rocks, as marble and chalk, from the shells of mollusks, 
or from coral ; or from clays that have originated by the 
chemical decomposition of feldspathic rocks containing 
much lime. 

Organic matter, especially the debris of former vegeta- 
tion, is almost never absent from the impalpable portion 
of the soil, existing there in some of the various forms as- 
sumed by humus. 

As Schone has shown, {Bulletin de la Societe des JSTatura- 
listes de Moscou, 1867, p. 363), the results obtained by 
Nobel's apparatus are far from answering the purposes of 
science. The separation is not carried far enough, and no 
simple relations subsist between the separated portions, as 
regards the dimensions of their particles. If the soil were 
composed of spherical particles of one kind of matter, or 



152 HOW CEOPS PEED. 

• 

having all the same specific gravity, it would be possible 
by the use of a properly constructed washing apparatus 
to separate a sample into fifty or one hundred parts, and 
to define the dimensions of the particles of each of these 
parts. Since, however, the soil is very heterogeneous, and 
since its particles are unlike in shape, consisting partly of 
nearly spherical grains and partly of plates or scales upon 
which moving water exerts an unequal floating effect, it is 
difficult, if not impossible, to realize so perfect a mechanic- 
al analysis. It is, however, easy to make a separation of a 
soil into a large number of parts, each of which shall ad- 
mit of precise definition in terms of the rapidity of flow 
of a current of water capable of sustaining the particles 
which compose it. Instruments for mechanical analysis, 
which provide for producing and maintaining at will any 
desired rate of flow in a stream of water, have been very 
recently devised, independentfy of each other, by E. Schone 
{loc. cit., pp. 334-405) and A. Muller ( Vs. St., X, 25-51). 
The employment of such apparatus promises valuable re- 
sults, although as yet no extended investigations made 
with its help have been published. 

Gravelly Soils are so named from the abundance of 
small stones or pebbles in them. This name alone gives 
but little idea of the really important characters of the 
soil. Simple gravel is nearly valueless for agricultural 
purposes ; many highly gravelly soils are, however, very 
fertile. The fine portion of the soil gives them their crop- 
feeding power. The coarse parts ensure drainage and 
store the solar heat. The mineralogical characters of the 
pebbles in a soil, as determined by a practised eye, may 
often give useful indications of its composition, since it 
is generally true that the finer parts of the soil agree in 
this respect with the coarser, or, if different, are not in- 
ferior. Thus if the gravel of a soil contains many pebbles 
of feldspar, the soil itself may be concluded to be well 
supplied with alkalies ; if the gravel consists of limestone, 



KINDS OF SOILS. 153 

we may infer that lime is abundant in the soil. On the 
other hand, if a soil contains a large proportion of quartz 
pebbles, the legitimate inference is that it is of compara- 
tively poor quality. The term gravelly admits of various 
qualification. We may have a very gravelly or a mod- 
erately gravelly soil, and the coarse material may be char- 
acterized as a fine or coarse gravel, a slaty gravel, a 
granitic gravel, or a diorite gravel, according to its state 
of division or the character of the rock from which it was 
formed. 

But the closest description that can thus be given of a 
gravelly soil cannot convey a very precise notion of even 
its external qualities, much less of those properties upon 
which its fertility depends. 

Sandy Soils are those which visibly consist to a large 
degree, 90" 1^ or more, of sand^ i. e., of small granular 
fragments of rock, no matter of what kind. Sand usually 
signifies grains of quartz-, this mineral, from its hardness, 
w^ith standing the action of disintegrating agencies beyond 
any other. Considerable tracts of nearly pure and white 
quartz sand are not uncommon, and are characterized by 
obdurate barrenness. But in general, sandy soils are by no 
means free from other silicious minerals, especially feldspar 
and mica. When the sand is yellow or red in color, this fact 
is due to admixture of oxide or silicates of iron, and points 
with certainty to the presence of ferruginous minerals or 
their decomposition-products, which often give considera- 
ble fertility to the soil. 

Other varieties of sand are not uncommon. In N'ew 
Jersey occur extensive deposits of so-called green sand, 
containing grains of a mineral, glauconite, to be hereafter 
noticed as a fertilizer. Ijime sand, consisting of grains 
of carbonate of lime, is of frequent occurrence on the 
shores of coral islands or reefs. The term sandy-soil is 
obviously very indefinite, including nearly the extremes 



154 HOW CROPS FEED. 

of fertility and barrenness, and covering a wide range of 
variety as regards composition. It is therefore qualified 
by various epithets, as coarse, fine, etc. Coarse, sandy 
soils are usually unprofitable, while fine, sandy soils are 
often valuable. 

^ Clayey Soils are those in which clay or impalpable mat- 
ters predominate. They are commonly characterized by 
extreme fineness of texture, and by great retentive ][X)wer 
for water ; thi^ liquid finding passage through their pores 
with extreme slowness. When dried, they become crack- 
ed and rifted in every direction from the shrinking that 
takes place in this process. 

It should be distinctly understood that a soil may be 
clayey without being clay, i. e., it may have the external, 
physical properties of adhesiveness and imi^ermeability to 
water which usually characterize clay, without containing 
those compounds (kaolinite and the like) which constitute 
clay in the true chemical sense. 

On the other hand it were possible to have a soil consist- 
ing chemically of clay, which should have the physical 
properties of sand ; for kaolinite has been found in crys- 
tals 5o'oo of an inch in breadth, and destitute of all cohesive- 
ness or plasticity. Kaolinite in such a coarse form is, how- 
ever, extremely rare, and not likely to exist in the soil. 

Loamy Soils are those intermediate in character between 
sandy and clayey, and consist of mixtures of sand with 
clay, or of coarse with impalpable matters. They are free 
from the excessive tenacity of clay, as well as from the too 
great porosity of sand. 

The gradations between sandy and clayey soils are 
roughly expressed by such terms and distinctions as the 
following : 





KINDS 


OF 


' SOILS. 


li 






aay 


or imjjolijable matters. 


Sand. 


Heavy day contains 








75-900 (o 


10— 250 lo 


Clay loam " 








60-75 


25—40 


Loam . 








40-60 


40— 60 


Sandy loayn *' 








25—40 


60— 75 


Light sandy loam contains 






10—25 


75— 90 



155 



Sand " 0—10 90—100 

The percentage composition above given applies to 
tlie diy soil, and must be received with great allowance, 
since the transition from fine sand to impalpable matter 
not physically distinguishable from clay, is an impercep- 
tible one, and therefore not well admitting of nice discrim- 
ination. 

It is furthermore not to be doubted that the difference 
between a clayey soil and a loamy soil depends more on 
the form and intimacy of admixture of the ingredients, 
than upon their relative proportions, so that a loam may 
exist which contains less sand than some clayey soils. 

Calcareous or Lime Soils are those in which carbonate 
of lime is a predominating or characteristic ingredient. 
They are recognizable by effervescing vigorously when 
drenched with an acid. Strong vinegar answers for test- 
ing them. They are not uncommon in Europe, but in this 
country are comparatively rare. In the ISTorthern and 
Middle States, calcareous soils scarcely occur to an extent 
worthy of mention. 

While lime soils exist containing 75° \^ and more of car- 
bonate of lime, this ingredient is in general subordinate 
to sand and clay, and Ave have therefore calcareous sands^ 
calcareous clays., or calcareous loams. 

Marls are mixtures of clay or clayey matters, with finely 
divided carbonate of lime, in something like equal propor- 
tions.* 

Peat or Swamp Muck is humus resulting from decayed 



* In New Jersey, green sand marl, or marl simply, is the name applied to the 
green sand employed as a fertilizer. SMI marl is a name designating nearly 
ptire carbonate of lime found in swamps. 



156 HOW CROPS FEED. 

vegetable matter in bogs and marshes. A soil is peaty or 
mucky when containing vegetable remains that have suf- 
fered partial decay under water. 

Vegetable Mold is a soil containing much organic mat- 
ter that has decayed without submergence in water, either 
resulting from the leaves, etc., of forest trees, from the 
roots of grasses, or from the frequent application of large 
doses of strawy manures. i 

Ochery or Ferruginous Soils are those containing much 
oxide or silicates of iron ; they have a yellow, red, or 
brown color. 

Other divisions are current among practical men, as, 
for example, surface and subsoil, active and inert soil, 
tilth, and hard pan. These terms mostly explain them- 
selves. When, at the depth of four inches to one foot or 
more, the soil assumes a different color and texture, these 
distinctions have meaning. 

The surface soil, active soil, or tilth, is the portion that 
is wrought by the instruments of tillage — that which is 
moistened by the rains, warmed by the sun, permeated by 
the atmosphere, in which the plant extends its roots, gath- 
ers its soil-food, and which, by the decay of the subter- 
ranean organs of vegetation, acquires a content of humus. 

Subsoil. — ^Where the soil originally had the same char- 
acters to a great depth, it often becomes modified down 
to a certain point, by the agencies just enumerated, in 
such a manner that the eye at once makes the distinction 
into surface soil and subsoil. In many cases, however, 
such distinctions are entirely arbitrary, the earth changing 
its appearance gradually or even remaining uniform to a 
considerable depth. Again, the surface soil may have a 
greater downward extent than the active soil, or the tilth 
may extend into the subsoil. 

Hard pan is the appropriate name of a dense, almost 
impenetrable, crust or stratum of ochery clay or com- 



PHYSICAL CHAKACTERS OF THE SOIL. 157 

pacted gravel, often underlying a fairly fruitful soil. It 
is the soil reverting to rock. The particles once disjointed 
are being cemented together again by the solutions of 
lime, iron, or alkali-silicates and humates that descend from 
the surface soil. Such a stratum often separates the sur- 
face soil from a deep gravel bed, and peat swamps thus 
exist in basins formed on the most porous soils by a thin 
layer of moor-hed-pan. 

With, these general notions regarding the origin and 
characters of soils, we may proceed to a somewhat extend- 
ed notice of the properties of the soil as influencing fertil- 
ity. These divide themselves into physical characters — 
those which externally affect the growth of the plant ; 
and chemical characters — those which provide it with food. 



CHAPTER IV. 
PHYSICAL CHARACTERS OF THE SOIL. 

The physical characters of the soil are those which con- 
cern the form and arrangement of its visible or palpable 
particles, and likewise include the relations of these parti- 
cles to each other, and to air and water, as well as to the 
forces of heat and gravitation. Of these physical char- 
acters we have to notice : 

1. The Weight of Soils. 

2. State of Division. 

3. Absorbent Power for Vapor of Water, or Hygro- 
scopic Capacity. 

4. Property of Condensing Gases. 

5. Power of fixing Solid Matters from their Solutions. 

6. Permeability to Liquid Water. Capillary Power. 

7. Changes of Bulk by Drying, etc. 

8. Adhesiveness. 

9. Relations to Heat. 



158 HOW CROPS FEED. 

In treating of the physical characters of the soil, the 
writer employs an essay on this subject, contributed by 
him to Yol. XVI of the Transactions of the "N. Y. State 
Agricultural Society, and reproduced in altered form in a 
Lecture given at the Smithsonian Institution, Dec, 1859. 

§ 1. 
THE WEIGHT OF SOILS. 

The Absolute Weight of Soils varies directly with their 
porosity, and is greater the more gravel and sand they 
contain. In the following Table is given the weight per 
cubic foot of various soils according to Schtibler, and like- 
wise (in round numbers) the weight per acre taken to the 
depth of one foot (=43,560 cubic feet). 



Weight 


OF 


Soils 










per cubic foot 


per acre 


5 to depth 








of one foot. 


Dry silicions or calcareous sand 


. about 


110 lbs 




4,792,000 


Half sand and half clay 






96 " 




4,182,000 


Common arable land * 




' SO to 


90 " 


3,485,000 


to 3,920,000 


Heavy clay 




75 " 




3,267,000 


Garden mold, rich in A'egetable matter. . 






TO " 




3,049^000 


Peat soil 




' 30 to 


50 '^ 


1,307,000 


to 2,178,000 



From the above figures we see that sandy soils, which 
are usually termed " light," because they are worked most 
easily by the plow, are, in fact, the heaviest of all ; while 
clayey land, which is called " heavy," weighs less, bulk 
for bulk, than any other soils, save those in which vegeta- 
ble matter predominates. The resistance offered by soils 
in tillage is more the result of adhesiveness than of gravity. 
Sandy soils, though they contain in general a less percent- 
age of nutritive matters than clays, may really offer as good 

* The author is indebted to Prof. Seely, of Middlebury, Vt., for a sample of 
one-fourth of a cubic foot of Wheat Soil from South Onondaga, New York. The 
cubic foot of this soil, when dry, weighs 86V2 lbs. The acre to depth of one foot 
weighs 3,768,000 lbs. This soil contains a large proportion of slaty gravel. A 
rich garden soil of silicious sand that had been heavily dunged, time out of 
mind, Boussingault found to weigh 81 lbs. av. per cubic foot (1.3 kilos per liter). 
This would be per acre, one foot deep, 3,528,000 lbs. 



PHYSICAL CHAKACTERS OF THE SOIL. 159 

nourishment to crops as the latter, since they present one- 
half more absolute weight in a given space. 

Peat soils are light in both senses ia which this word 
is used by agriculturists. 

The Specific Gravity of Soils is the weight of a given 
bulk compared with the same bulk of water. A cubic 
foot of water weighs 62^ lbs., but comparison of this num- 
ber with the numbers stated in the last table expressing 
the weights of a cubic foot of various soils does not give 
us the true specific gravity of the latter, for the reason 
that these weights are those of the matters of the soil 
contained in a cubic foot, but not of a cubic foot of these 
matters themselves exclusive of the air, occupying their 
innumerable interspaces. When we exclude the air and 
take account only of the soil, we find that all soils, except 
those containing very much humus, have nearly the same 
density. Schone has recently determined with care the 
specific gravity of 14 soils, and the figures range from 
2.53 to 2.71. The former density is that of a soil rich iu 
humus, from Orenberg, Russia ; the latter of a lime soil 
from Jena. The density of sandy and clayey soils free from 
humus is 2.65 to 2.69. {Bulletin de la Soc. Imp. des 
JVaturalistes de Jfoscou, 1867, p. 404.) This agrees with 
the density of those minerals which constitute the bulk 
of most soils, as seen from the following statement of their 
specific gravity, which is, for quartz, 2.65; feldspar, 2.62; 
mica, 2.75-3.10 ; kaolinite, 2.60. Calcite has a sp. gr. of 
2.72 ; hence the greater density of calcareous soils. 

§2. 

STATE OF DIVISION OF THE SOIL AND ITS INFLUENCE ON 
FERTILITY. 

On the surface of a block of granite only a few lichens 
and mosses can exist ; crush the block to a coarse powder 
and a more abundant vegetation can be supported on it ; 



160 now CKors feed. 

if it is reduced to a very fine dust and duly watered, even 
the cereal grains will grow and perfect fruit on it. 

Magnus {Jour, far prdkt. Ghem.^ L, 70) caused barley 
to germinate in pure feldspar, which was in one experi- 
ment coarsely,. in another finely, pulverized. In the coarse 
feldspar the plants grew to a height of 15 inches, formed 
ears, and one of them ripened two perfectly formed seeds. 
In the fine feldspar the plants were very decidedly strong- 
er. One of them attained a height of 20 inches, and 
produced four seeds. 

It is true, as a general rule, that all fertile soils contain 
a large proportion of fine or impalpable matter. The soil 
of the " Ree Ree Bottom," on the Scioto River, Ohio, re- 
markable for its extraordinary fertility, which has remained 
nearly undiminished for 60 years, though yielding heavy 
crops of wheat and maize without interruption, is char- 
acterized by the fineness of its particles. (D. A. Wells, 
Am, Jour. jSci., XIV, 11.) In what way the extreme di- 
vision of the particles of the soil is connected with its fer- 
tility is not difficult to understand. The food of the plant 
as existing in the soil must pass into solution either in the 
moisture of the soil, or in the acid juices of the roots of 
plants. In either case the rapidity of its solution is in 
direct ratio to the extent of surface which it exposes. 
The finer the particles, the more abundantly will ilje plant 
be supplied with its necessary nourishment. In the Scioto 
valley soils, the water which surrounds the roots of tho 
crops and the root-fibrils themselves come in contact with 
such an extent of surface that they are able to dissolve 
the soil-ingredients in as large quantity and as rapidly as 
the crop requires. In coarse-grained soils this is not so 
likely to be the case. Soluble matters (manures) must be 
applied to them by the farmer, or his crops refuse to yield 
handsomely. 

It is furthermore obvious, that, other things being equal, 
the finer the, articles of the soil the more space the grow- 



PHYSICAL CHARACTERS OF THE SOIL. 161 

ing roots have in which to expand themselves, and the 
more abundantly are they able to present their absorbent 
surfaces to the supplies which the soil contains. The fine- 
ness of the particles may, however, be excessive. They 
may fit each other so closely as to interfere with the 
growth of the roots, or at least with the sprouting of the 
seed. The soil may be too compact. 

It will presently appear that other very important prop- 
erties of the soil are more or less related to its state of 
mechanical division. 

§ 3. 

ABSORPTION OF VAPOR OF WATER BY THE SOIL. 

The soil has a power of withdrawing vapor of water 
from the air and condensing the same in its pores. It is, 
in other words, hygroscopic. 

This property of a soil is of the utmost agricultural im- 
portance, because, 1st, it is connected with the permanent 
moisture which is necessary to vegetable existence ; and, 
2d, since the absorption of water-vapor to some degree 
determines the absorption of other vapors and gases. 

In the following table we have the results of a series 
of experiments carried out by Schiibler, for the purpose 
of determining the absorptive power of different kinds of 
earths and soils for vapor of water. 

The column of figures gives in thousandths the quantity 
of hygroscopic moisture absorbed in twenty-four hours by 
the previously dried soil from air confined over water, 
and hence nearly saturated with vapor. 

Quartz sand, coarse 

Gypsum 1 

Lime sand 3 

Plough land 23 

Clay soil, (60 per cent clay) 28 

Slaty marl 33 

Loam 35 



162 HOW CKOPS FEED. 

Fine carbonate of lime 35 

Heavy clay soil, (80 per cent clay) 41 

Garden mold, (7 per cent humus) 53 

Pure clay 49 

Carbonate of magnesia (fine powder) 83 

Humus 120 

Davy found that one thousand parts of the soils named 

below, after having been dried at 212°, absorbed during 

one hour of exposure to the air, quantities of moisture as 

follows : 

Sterile soil of Bagsliot heath 3 

Coarse sand 8 

Fine sand , 11 

Soil from Mersey, Essex =., 13 

Very fertile alluvium, Somersetshire 16 

Extremely fertile soil of Ormiston, East Lothian 18 

An obvious practical result follows from the facts ex- 
pressed in the above tables, viz.: that sandy soils which 
have little attractive force for watery vapor, and are there- 
fore dry and arid, may be meliorated in this respect by 
admixture with clay, or better with humus, as is done by 
dressing with vegetable composts and by green manuring. 
The first table gives us proof that gypsum does not exert 
any beneficial action in consequence of directly attracting 
moisture. Humus, or decaying vegetable matter, it will 
be seen, surpasses every other ingredient of the soil in 
absorbing vapor of water. This is doubtless in some de- 
gree connected with its extraordinary porosity or amount 
of surface. How the extent of surface alone may act is 
made evident by comparing the absorbent power of car- 
bonate of lime in the two states of sand and of an im- 
palpable powder. The latter, it is seen, absorbed twelve 
times as much vapor of water as the former. Carbonate 
of magnesia stands next to humus, and it is worthy of 
note that it is a very light and fine powder. 

Finally, it is a matter of observation that " silica and 
lime in the form of coarse sand make the soil in which 
they predominate so dry and hot that vegetation perishes 



PHYSICAL CHARACTERS OF THE SOIL. 163 

from want of moisture ; when, however, they occur asjine 
dust, they form too wet a soil, in which plants suffer from 
the opposite cause." — {Jlamm'^s I^cmdwirthschcfft.) 

Every body has a definite power of condensing moist- 
ure upon its surface or in its pores. Even glass, though 
presenting to the eye a perfectly clean and dry surface, is 
coated with a film of moisture. If a piece of glass be 
weighed on a very delicate balance, and then be wijDcd 
with a clean cloth, it will be found to weigh perceptibly 
less than before. Exposed to the air for an hour or more, 
it recovers the weight which it had lost by wiping; this 
loss was water. (Stas. Magnus.) The surface of the 
glass is thus proved to exert towards vapor of water an 
adhesive attraction. 

Certain compounds familiar to the chemist attract water 
with great avidity and to a large extent. Oil of vitriol, 
phosphoric acid, and chloride of calcium, gain weight rap- 
idly when exposed to moist air, or when placed contiguous 
to other substances which are impregnated with moisture. 
For this reason these compounds are employed for pur- 
poses of drying. Air, for example, is perfectly freed from 
vapor of water by slowly traversing a tube containing 
lumps of dried chloride of calcium, or phosphoric acid, or 
by bubbling repeatedly through oil of vitriol contained 
in a suitable apparatus. 

Solid substances, which, like chloride of calcium, carbon- 
ate of potash, etc., gather water from the air to such an 
extent as to become liquid, are said to deliquesce or to be 
deliquescent. Certain compounds, such as urea, the char- 
acteristic ingredient of human urine, deliquesce in moist 
air and dry away again in a warm atmosphere. 

Allusion has been made in " How Crops Grow," p. 55, 
to the hygroscopic water of vegetation, which furnishes 
another striking illustration of the condensation of water 
in porous bodies. 

The absorption of vapor of water by solid bodies is not 



164 HOW CROPS PEED. 

only dependent on the nature of the substance and its 
amount of surface, but is likewise influenced by external 
conditions. 

The rapidity of absorption depends upon the amount 
of vapor present or accessible, and is greatest in moist 
air. 

The amount of absorption is determined solely by tem- 
perature, as Knop has recently shown, and is unafiected 
by the relative abundance of vapor : i. e., at a given tem- 
perature a dry soil will absorb the same amount of moist- 
ure from the air, no matter whether the latter be slightly 
or heavily impregnated with vapor, but will do this the 
more speedily the more moist the surrounding atmosphere 
happens to be. 

In virtue of this hygroscopic character, the soil which 
becomes dry superficially during a hot day gathers water 
from the atmosphere in the cooler night time, even when 
no rain or dew is deposited upon it. 

In illustration of the influence of temperature on the 
quantity of water absorbed, as vapor, by the soil, we give 
Knop's observations on a sandy soil from Moeckern, Sax- 
ony: 

1,000 parts of this soil absorbed 

At 55° F. 13 parts of hygroscopic water. 
'' 66° " 11.9 " " " " 

U iri^'O t< -I Q 2 " " " '« 

Knop calculates on the basis of his numerous observa- 
tions that hair and wool, which are more hygroscopic than 
most vegetable and mineral substances, if allowed to ab- 
sorb what moisture they are capable of taking up, contain 
the following quantities of water, per cent, at the temper- 
atures named : 

At 87° Fah., 7.7 per cent. 
" 55° " 15.5 " " 
" 32° " 19.3 " " 



PHYSICAL CHAKACTEKS OF THE SOIL. 165 

Silk is sold in Europe by weight with suitable allowance 
for hygroscoj^ic moisture, its variable content of which is 
carefully determined by experiment in each important 
transaction. It is plain that the circumstances of sale 
may affect the weight of wool to 10 or more per cent. 

§4. 
CONDENSATION OF GASES BY THE SOIL. 

Adhesion. — In the fact that soils and porous bodies gen- 
erally have a physical absorbing power for the vapor of 
water, we have an illustration of a principle of very wide 
application, viz., The surfaces of liquid and solid matter 
attract the particles of other kinds of matter. 

This force of adhesion, as it is termed, when it acts up- 
on gaseous bodies, overcomes to a greater or less degree 
their expansive tendency, and coerces them into a smaller 
space — condenses them. 

Absorbent Power of Charcoal, etc.— Charcoal serves 
to illustrate this fact, and some of its most curious as well 
as useful properties depend upon this kind of physical 
peculiarity. Charcoal is prepared from wood, itself ex- 
tremely porous,* by expeUing the volatile constituents, 
whereby the porosity is increased to an enormous extent. 

When charcoal is kept in a damp cellar, it condenses so 
much vapor of water in its pores that it becomes difficult 
to set on fire. It may even take up one-fourth its own 
weight. When exposed to various gases and volatile 
matters, it absorbs them in the same manner, though to 
very unequal extent. 

De Saussure was the first to measure the absorbing 
power of charcoal for gases. In his experiments, boxwood 
charcoal was heated to redness and plunged under mer- 

* Mitscherlich has calculated that the cells of a cubic inch of boxwood have 
no less than 73 square feet of surface. 



166 HOW CEOPS FEED. 

ciiry to cool. Then introduced into the various gases 
named below, it absorbed as many times its bulk of them, 
as are designated by the subjoined figures : 

Ammonia 90 Hydrochloric acid 85 

Sulphurous acid 65 Hydrosulphuric acid 55 

Protoxide of nitrogen 40 Carbouic acid 35 

Ox3'gen 9)^ Carbonic oxide 9)4 

Hydrogen IM Nitrogen 7}4 

According to De Saussure, the absorption was complete 
in 24 hours, except in case of oxygen, where it continued for 
a long time, though with decreasing energy. The oxygen 
thus condensed in the charcoal combined with the carbon 
of the latter, forming carbonic acid. 

Stenhouse more lately has experimented in the same di- 
rection. From these regearches we learn that the power 
in question is exerted towards different gases with very 
unequal effect, and that different kinds of charcoal exert 
very different condensing power. 

Stenhouse found that one gramme of dry charcoal ab- 
sorbed of several gases the number of cubic centimeters 
given below. 



I^ame of Gas. 



Ammonia 

Hydrochloric acid — 
Hydrosulphuric acid. 

Sulphurous acid 

Carbonic acid 

Oxygen 



Kind of Charcoal. 


Wood. 


Peat. 


Animal. 


98.5 


96.0 


43.5 


45.0 


60.0 




30.0 


28.5 


9.0 


32.5 


27.5 17.5 


14.0 


10.0 5.0 


0.8 


0.6 


0.5 



The absorption or solution of gases in water, alcohol, 
and other liquids, is analogous to this condensation, and 
those gases which are most condensed by charcoal are in 
general, though not invariably, those which dissolve most 
copiously in liquids, (ammonia, hydrochloric acid). 

Condensation of Gases by the Soil. — Reichardt and 
Blumtritt have recently made a minute study of the kind 
and amount of gases that are condensed in the pores of 
various solid substances, including soils and some of their 



PHYSICAL CHAKACTERS OP THE SOIL. 167 

ingredients. {Jour, filr praJct. Chem.^ Bd. 98, p. 476.) 
Their results relate chiefly to these substances as ordinarily- 
occurring exposed to the atmosphere, and therefore more 
or less moist. The following Table includes the more im- 
portant data obtained by subjecting the substances to a 
temperature of 284° F., and measuring and analyzing the 
gas thus expelled. 







100 Grams 10 Vols, 
yielded gas yielded 
in vols. 
C. C. gas. 


100 Vols, of 


Gas contained : 


Substance : 


Nitro- 
gen. 


Oxy- 
gen. 


Carbon- 
ic acid. 


• Car- 
bonic 
oxide. 


Charcoal, air-drj'. 






164 


— 


100 











" moistened and dried i 


igain, 


,140 


59 


86 


2 


9 


3 


Peat, 






163 


— 


44 


5 


51 





Garden soil, moist, 






14 


20 


64 


3 


24 


9 


" " air-dry. 






38 


54 


65 


2 


33 





Hs^drated oxide of iron, air 


-dry, 




3T5 


309 


26 


4 


70 





Oxide of iron, ignited. 






39 


52 


83 


13 


4 





Hydrated alumina, air-dry, 






69 


82 


41 





59 


— 


Alumina, dried at Sia'', 






11 


14 


83 


17 





— 


Clay, 






33 


— 


65 


21 


14 


_ 


" long exposed to air. 






26 


39 


70 


5 


25 


— 


*' moistened, 






29 


35 


60 


6 


34 


— 


River silt, air-dry. 






40 


48 


08 





18 


14 


" " moistened. 






24 


29 


67 





31 


2 


" " again dried. 






26 


30 . 


67 


9 


16 


7 


Carbonate of lime (whiting 


,) 1864, 


43 


52 


100 








— 


" " " " 


1865, 


39 


48 


74 


16 


10 


— 


" " " precipitated. 


1864, 


65 


— 


81 


19 





— 


U (1 i( (( 




1865, 


51 


52 


77 


15 


8 





Carbonate of magnesia. 






729 


125 


64 


7 


29 





Gypsum, pulverized, 






17 


— 


81 


19 





— 



From these figures we gather : 

1. The gaseous mixture which is contained in the pores 
of solid substances rarely has the composition of the at- 
mosphere. In but two instances, viz., with gypsum and 
precipitated carbonate of lime., were only oxygen and ni- 
trogen absorbed in pro^^ortions closely approaching those 
of the atmosphere. 

2. Nitrogen appears to bo nearly always absorbed in 
greater proportion than oxygen, and is greatly condensed 
in some cases, as by peat, hydrated oxide of iron, and car- 
bonate of magnesia. 



168 HOW CROPS FEED. 

8. Oxygen is often nearly or quite wanting, as in char- 
coal, oxide of iron, alumina, river silt, and whiting. 

4. Carbonic acid, though sometimes wanting entirely, 
is usually abundant in the absorbed gases. 

5. In the pores of charcoal and of soils containing de- 
caying organic matters, carbonic acid is often partially re- 
placed by carbonic oxide. The experiments, however, do 
not furnish proof that this substance is not formed under 
the influence of the high temperature employed (28-4° F.) 
in expelling the gases, rather than by incomplete oxidation 
of organic matters at ordinary temperatures. 

6. A substance, when moist, absorbs less gas than when 
dry. In accordance with this observation, De Saussure no- 
ticed that dry charcoal saturated with various gases evolv- 
ed a good share of them when moistened with water. 
Ground (and burnt ?) coffee, as Babinet has lately stated, 
evolves so much gas when drenched with water as to burst 
a bottle in which it is confined. 

The extremely variable figures obtained by Blumtritt 
when operating with the same substance (the figures given 
in the table are averages of two or three usually discordant 
results), result from the general fact that the proportion 
in which a number of gases are present in a mixture, in- 
fluences the proportion of the individual gases absorbed. 
Thus while charcoal or soil will absorb a large amount of 
ammonia from the pure gas, it will take up but traces of 
this substance from the atmosphere of which ammonia is 
but an infinitesimal ingredient. 

So, too, charcoal or soil saturated with ammonia by ex- 
posure to the unmixed gas, loses nearly all of it by stand- 
ing in the air for some time. This is due to the fact that 
gases attract each otliev^ and the composition of the gas 
condensed in a porous body varies perpetually with the 
variations of composition in the surrounding atmosphere. 

It is especially the water-gas (vapor of water) which is 
a fluctuating ingredient of the atmosphere, and one which 



PHYSICAL CHARACTERS OF THE SOIL. 169 

is absorbed by porous bodies in the largest quantity. 
This not only displaces other gases from their adhesion to 
solid surfaces, but by its own attractions modifies these 
adhesions. 

Reichardt and Blumtritt take no account of water-gas, 
except in the few experiments where the substances were 
purposely moistened. In all their trials, however,* moist- 
ure was present, and had its quantity been estimated, 
doubtless its influence on the extent and kind of absorp- 
tion would have been strikingly evident throughout. 

Ammonia and carbonate of ammonia in the gaseous 
form are absorbed from the air by the dry soil, to a less 
degree than by a soil that is moist, as will be noticed fully 
hereafter. 

Chemical Action induced by Adhesion,— This physical 
property often leads to remarkable chemical effects ; in 
other words, adhesion exalts or brings into play the force 
of affinity. When charcoal absorbs those emanations 
from putrefying animal matters wliich we scarcely know, 
save by their intolerable odor and poisonous influence, it 
causes at the same time their rapid and complete oxida- 
tion ; and hence a piece of tainted meat is sweetened by 
covering it with a thin layer of powdered charcoal. As 
Stenhousc has shown, the carcass of a small animal may 
be kept in a living-room during the hottest weather with- 
out giving off any putrid odor, provided it be surrounded 
on all sides by a layer of powdered charcoal an inch or 
more thick. Thus circumstanced, it simply smells of am- 
monia, and its destructible parts are resolved directly in- 
to water, carbonic acid, free nitrogen, and ammonia, pre- 
cisely as if they were burned in a furnace, and without 
the appearance of any of the effluvium that ordinarily 
arises from decaying flesh. 

The metal platinum exhibits a remarkable condensing 
power, which is manifest even with the polished surface of 
foil or wire; but is most striking when the metal is 
8 



170 now cKors feed. 

brought to the condition of sponge, a form it assumes 
when certain of its compounds (e. g. ammonia-chloride of 
platinum) are decomposed by lieat, or to the more finely 
divided state of platinum black. The latter is capable of 
condensing from 100 to 250 times its volume of oxygen, 
according to its mode of preparation (its porosity ?) ; and 
for this reason it possesses intense oxidizing power, so that, 
for example, when it is brought into a mixture of oxygen 
and hydrogen, it causes them to unite explosively. A jet 
of hydrogen gas, allowed to play on platinum sponge, is 
almost instantly ignited — a fact taken advantage of in 
Dobereiner's hydrogen lamp. 

The oxidizing powers of platinum are much more vig- 
orous than those of charcoal Stenhouse has proposed 
the use of i)latinized charcoal (charcoal ignited after moist- 
ening with solution of chloride of platinum) as an escha- 
rotic and disinfectant for foul ulcers, and has shown that 
the foul air of sewers and vaults is rendered innocuous 
when filtered or breathed through a layer of this material.* 

Chemical Action a Result of the Porosity of the Soil. 
— From these significant facts it has been inferred that the 
soil by virtue of the extreme porosity of some of its ingre- 
dients is the theater of chemical changes of the utmost 
importance, which could not transpire to any sensible ex- 
tent but for this high division of its particles and the vast 
surface tliey present. 

The soil absorbs putrid and other disagreeable effluvia, 
and undoubtedly oxidizes theni like charcoal, though, per- 
haps, with less energy than the last named substance, as 
would be anticipated from its inferior porosity. Garments 
which have been rendered disgusting by the fetid secre- 
tions of the skunk, may be " sweetened," i. e. deprived of 



* Platinum docs not condense hydrogen gas ; but the metal PaUadium, which 
occurs associated with platinum, has a most astonishing absorptive power for 
hydrogen, being able to take up or "occlude" 900 limes its volume of the gas, 
(Graham, Proceedings Boy. i>oc., 1868^ p. 422.) 



ABSORBENT POWER OF SOILS. 171 

odor, by burying them for a few days in the earth. The 
Indians of this country are said to sweeten the carcass of 
the skunk by the same process, when needful, to fit it for 
their food. Dogs and foxes bury bones and meat in the 
ground, and aftervC^ard exhume them in a state of com- 
parative freedom from offensive odor. 

When human excrements are covered with fine dry 
earth, as in the "Earth Closet" system, all odor is at once 
suppressed and never reappears. At the most, besides an 
"earthy" smell, an odor of ammonia appears, resulting 
from decomposition, which appears to proceed at once to 
its ultimate results without admitting of the formation of 
any intermediate offensive compounds. 

Dr. Angus Smith, having frequently observed the pres- 
ence of nitrates in the water of shallow town wells, sus- 
pected that the nitric acid was derived from animal mat- 
ters, and to test this view, made experiments on the action 
of filters of sand, and other porous bodies, upon solutions 
of dififerent animal and vegetable matters. He found 
that in such circumstances oxidation took place most rap- 
idly — the nitrogen of organic matters being converted in- 
to nitric acid, the carbon and hydrogen combining with 
oxygen at the same time. Thus a solution of yeast, which 
contained no nitric acid, after being passed through a 
filter of sand, gave abundant evidence of salts of this acid. 
Colored solutions were in this way more or less decolor- 
ized. Water, rendered brown by peaty matter, was found 
to be purified by filtration through sand.* 

§ 5. 

POWER OF SOILS TO REMOVE DISSOLVED SOLIDS FROM 
THEIR SOLUTIONS. 

Action of Sand upon Saline Solutions.— It has long 
been known that simple sand is capable of partially re- 

* This account of Dr. Smith's experiments is quoted from Prof. Way's paper 
" On the Power of Soils to Absorb Manure." {Jmr. Roy. Ag. Soc. of EnglarKl, 
XI, p. 317.) 



172 HOW CROPS FEED. 

moving saline matters from their solutions in water. Lord 
Bacon, in his " Sylva Sylvarum," speaks of a method of 
obtaining fresh water, which was practised on the coast 
of Barbary. " Digge a hole on the sea-shore somewhat 
above high-water mark and as deep as low-water mark, 
which, when the tide cometh, will be filled with water 
fresh and potable." He also remarks " to have read that 
trial hath been made of salt-water passed through earth 
through ten vessels, one within another, and yet it hath 
not lost its saltness as to become potable ; " but when 
" drayned through twenty vessels, hath become fresh." 

Dr. Stejihen Hales, in a j^aper read before the Royal 
Society in 1739, on " Some attempts to make sea-water 
wholesome," mentions on the authority of Mr. Boyle God- 
frey that "sea-water, being filtered through stone cisterns, 
the first pint that runs through will be pure water having 
no taste of the salt, but the next pint will be salt as usual." 

Berzelius found upon filtering solutions of common salt 
through sand, that the portions which first passed were 
quite free from saline impregnation. Matteucci extended 
this observation to other salts, and found that the solu- 
tions when filtered through sand were diminished in den- 
sity, showing a detention by the sand of certain quantities 
of the salt operated upon.* 

Action of Humus on Saline Solutions. — Heiden {Soff- 
mamibS Jahreshericht, 1866, p. 29) found that peat and 
various preparations of the humic acids, when brought in- 
to solutions of chloride of potassium and chloride of am- 
monium, remove a portion of these salts from the liquid, 
leaving the solutions perceptibly weaker. The removed 
salts Avere for the most part readily dissolved by a small 
quantity of water. W. Schumacher {Hoff. Jahres.^ 1867, 
p. 18) observed that humus, artificially prepared by the 

* These statements of Bacon, Hales, Berzelius, and Matteucci, are derived 
from Prof. Way's paper " On thje Power of Soils, etc." (Jmr. Boy. Ag. Soc. of 
Eng., XI, 316.) 



ABSORBENT POWER OF SOILS. 173 

action of oil of vitriol on sugar, when placed in ten times 
its quantity of solutions of various salts (containing about 
^ per cent of solid matter) absorbed of sulphates of soda 
and ammonia, and chlorides of calcium and ammonium, 
about 2 per cent ; of sulphate of potash 4 per cent ; and of 
phosphate of soda 10 per cent. Schumacher also noticed 
that sulphate of potash is able to expel sulphate of ammo- 
nia from humic acid which has been saturated with the 
latter salt, but that the latter cannot displace the former. 
In Schumacher's experiments, pure water freely dissolved 
the salts absorbed by the humic acid. 

Explanation. — Let us consider what occurs in the act 
of solution and in this separation of soluble matters from 
a liquid. The difference between the solid and the liquid 
state, so far as we can define it, lies in the unequal cohe- 
sion of the particles. Cohesion prevails in solids, and op- 
poses freedom of motion among the jjarticles. In liquids, 
cohesion is not altogether overcome but is greatly weak- 
ened, and the particles move easily upon each other. 
When a lump of salt is put into water, the cohesion that 
otherwise maintains its particles in the solid state is over- 
come by the attraction of adhesion, which is mutually ex- 
erted between them and the particles of water, and the 
salt dissolves. If now into the solution of salt any in- 
soluble solid be placed which the liquid can wet (adhere 
to) its particles will exert adhesive attraction for the par- 
ticles of salt, and the tendency of the latter will be to 
concentrate somewhat upon the surface of the solid. 

If the sol^l, thus introduced into a solution, be exceed- 
ingly porous, or otherwise present a great amount of sur- 
face, as in case of sand or humus, this tendency is propor- 
tionately heightened, and a separation of the dissolved 
substance may become plainly evident on proper examina- 
tion. When, on the other hand, the solid surface is rela- 
tively small, no weakening of the solution may be percep- 
tible by ordinary means. Doubtless the glass of a bottle 



174 HOW CROPS FEED. 

containing brine concentrates the latter where the two 
are in contact, though the eifect may be difficult to dem- 
onstrate. 

Defecating Action of Cliarcoal on Solutions. — Char- 
coal manifests a strong surface attraction for various 
solid substances, and exhibits this power by overcoming 
the adhesion they have to the particles of water when dis- 
solved in that fluid. If ink, solution of indigo, red wine, 
or bitter ale, be agitated some time with charcoal, the 
color, and in the case of ale, the bitter principle, will be 
taken up by the charcoal, leaving the liquid colorless and 
comparatively tasteless. Water, which is impure from 
putrefying organic matters, is sweetened, and brown sugars 
are whitened by the use of charcoal or bone-black. In 
case of bone-black, the finely divided bone-earth (phos- 
phate of lime) assists the action of the charcoal. 

Fixing of Dye-Stuffs. — The familiar process of dyeing 
depends upon the adhesion of coloring matters to the fiber 
of textile fabrics. Wool steeped in solution of indigo at- 
taches the pigment permanently to its fibers. Silk in the 
same way fastens the particles of rosaniline, which consti- 
tutes the magenta dye. Many colors, e. g. madder and 
logwood, which will not adhere themselves directly to 
cloth, are made to dye by the use of mordants — substances 
like alumina, oxide of tin, etc. — which have adhesion both 
to the fabric and the pigment. 

Absorptive Power of Clay. — These effects of charcoal 
and of the fibers of cotton, etc., are in great part identical 
with those previously noticed in case of sand and humus. 
Their action is, however, more intense, and the effects 
are more decided. Charcoal, for example, that has ab- 
sorbed a pigment or a bitter principle from a liquid, -will 
usually yield it up again to the same or a stronger solvent. 
In some instances, however, as in dyeing with simple col- 
ors, matters are fixed in a state of great permanence by 



ABSORBENT POWER OF SOILS. 175 

the absorbent ; and in others, as where mordants are used, 
chemical combinations supervene, which possess extraordi- 
nary stability. 

Many facts are known which show that soils, or certain 
of their ingredients, have a fixing power like that of char- 
coal and textile fibers. It is a matter of comfnon expe- 
rience that a few feet or yards of soil intervening between 
a cess-pool or dung-pit, and a well, preserves the latter 
against contamination for a longer or shorter period. 

J. P. Bronner, of Baden, in a treatise on " Grape Cul- 
ture in South Germany," published in 1836, first mentions 
that dung liquor is deodorized, decolorized, and rendered 
nearly tasteless by filtration through garden earth. Mr. 
Huxtable, of England, made the same observation in 1848, 
and Prof Way and others have published extended in- 
vestigations on this extremely important subject. 

Prof Way informs us that he filled a long tube to the 
depth of 18 inches with Mr. Huxtable's light soil, mixed 
with its own bulk of white sand. " Upon this filter-bed 
a quantity of highly ofiensive stinking tank water was 
poured. The liquid did not pass for several hours, but 
ultimately more than 1 ounce of it passed quite cleai\ free 
from smell or taste^ except a peculiar earthy smell and 
taste derived from the soil." Similar results were obtain- 
ed by acting upon putrid human urine, upon the stinking 
water in which flax had been steeped, and upon the water 
of a London sewer. 

Prof Way found that these effects were not strikingly 
manifested by pure sand, but appeared when clay was 
used. He found that solutions of coloring matters, such 
as logwood, sandal-wood, cochineal, litmus, etc., when fil- 
tered through or shaken up with a portion of clay, are 
entirely deprived of color. {Jour. Roy. Ag. Soc. of 
Mig., XI, p. 364.) 

These effects of clay or clayey matters, like the fixing 
power of cotton and woolen stuffs upon pigments, must 



176 HOAV CROPS FEED. 

be regarded for the most pcart us purely j^hysical. There 
are other results of the action of the soil on saline solu- 
tions, which, though perhaps influenced hy simple physical 
action, are preponderatingly chemical in their aspect. 
These eflects, which manifest themselves by chemical de- 
compositions and substitutions, will be fully discussed in 
a subsequent chapter, p. 333. 

§ 6- 

PERMEABILITY OF SOILS TO LIQUID WATER. IMBIBITION. 
CAPILLARY POWER. 

The fertility of the soil is greatly influenced by its de- 
portment toward water in the liquid state. 

A soil \.^ permeable to water when it allows that liquid 
to soak into or run through it. To be permeable is of 
course to be porous. On the size of the pores depends its 
degree of permeability. Coarse sands, and soils which 
have few but large pores or interspaces, allow water to 
run through them readily — water percolates them. When, 
instead of running through, the water is largely absorbed 
and held by the soil, the latter is said to possess great 
capillary power ^ such a soil has tnany and minute pores. 
The cause of capillarity is the same surface attraction 
which has been already under notice. 

When a narrow vial is jDartly filled with water, it will 
be seen that the liquid adheres to its sides, and if it be not 
more than one-half inch in diameter, the surface of the 
liquid Avill be curved or concave. In a very narrow tube 
the liquid will rise to a considerable height. In these 
cases the surface attraction of the glass for the water neu- 
tralizes or overcomes the weight of (earth's attraction for) 
the latter. 

The pores of a sponge raise and hold water in them, in 
the same way that these narrow (capillary *) tubes sup- 

* From capUlus, the Latin word for hair, because as fine as hair ; (but a hair is 
no tube, as is often supposed.) 



PEKMEABILITY OF SOILS TO LIQUID WATER. 177 

port it. When a body has pores so fine (surfaces so near 
each other) that their surface attraction is greater than 
the gravitating tendency of water, then the body will im- 
bibe and hold water — will exhibit capillarity ; a lump of 
salt or sugar, a lamp-wick, are familiar examples. When 
the pores of a body are so large (the surfaces so distant) 
that they cannot fill themselves or keep themselves full, 
the body allows the water to run through or to percolate. 

Sand is most easily permeable to water, and to a higher 
degree the coarser its particles. Clay, on the other hand, 
is the least penetrable, and the less so the purer and more 
plastic it is. 

When a soil is too coarsely porous, it is said to be leachy 
or hungry. The rains that fall upon it quickly soak 
through, and it shortly becomes dry. On such a soil, the 
manures that may be applied in the spring are to some de- 
gree washed down below the reach of vegetation, and in 
the droughts of summer, plants suffer or perish from Avant 
of moisture. 

When the texture of a soil is too fine, — its pores too 
small, — as happens in a heavy clay, the rains penetrate it 
too slowly ; they flow off the surface, if the latter be in- 
clined, or remain as pools for days and even weeks in the 
hollows. 

In a soil of proper texture the rains neither soak off into 
the under-earth nor stagnate on the surface, but the soil 
always (except in excessive wet or drought) maintains 
the moistness which is salutary to most of our cultivated 
plants. 

Movements of Water in the Soil. — If a wick be put 
into a lamp containing oil, the oil, by capillary action, 
gradually permeates its whole length, that which is above 
as well as that below the surface of the liquid. When the 
lamp is set burning, the oil at the flame is consumed, and 
as each particle disappears its place is supplied by a new 
one, until the lamp is empty or the flame extinguished. 
8* 



178 HOW CKOPS FEED. 

Something quite analogous occurs in the soil, by wliich 
the plant (corresponding to the flame in our illustration) is 
fed. The soil is at once lamp and wick, and the water of 
the soil represents the oil. Let evaporation of water from 
the surface of the* soil or of the plant take the place of 
the combustion of oil from a wick, and the matter stands 
thus : Let us suppose dew or rain to have saturated the 
ground with moisture for some depth. On recurrence of ^ 
a dry atmosphere with sunshine and wind, the surface of 
the soil rapidly dries ; but as each particle of water es- 
capes (by evaporation) into the atmosphere, its place is 
supplied (by capillarity) from the stores below. The as- 
cending water brings along with it the soluble matters of 
the soil, and thus the roots of plants are situated in a 
stream of their appropriate food. The movement i:>roceeds 
in this way so long as the surface is drier than the deej^er 
soil. When, by rain or otherwise, the surface is saturated, 
it is like letting a thin stream of oil run upon the apex of 
the ] amp-wick — no more evaporation into the air can oc- 
cur, and consequently there is no longer any ascent of 
water ; on the contrary, the water, by its own weight, 
penetrates the soil, and if the underlying ground be not 
saturated with moisture, as can happen where the subter- 
ranean fountains yield a meagre supply, then capillarity 
will aid gravity in its downward distribution. 

It is certain that a portion of the mineral matters, and, 
perhaps, also some organic bodies which feed the plant, 
are more or less freely dissolved in the water of the soil. 
So long as evaporation goes on from the surface, so long 
there is a constant upward flow of these matters. Those 
portions which do not enter vegetation accumulate on or 
near the surface of the ground ; when a rain falls, they are 
washed down again to a certain depth, and thus are kept 
constantly changing their place with the water, which is 
the vehicle of their distribution. In regions where rain 
falls periodically or not at all, this upward flow of the soil- 



PERMEABILITY OF SOILS TO LIQUID WATER. 179 

water often causes an accumulation of salts on the surface 
of the ground. Thus in Bengal many soils which in the 
wet season produce the most luxuriant crops, during the 
rainless portion of the year become covered with white 
crusts of saltpeter. The beds of nitrate of soda that are 
found in Peru, and the carbonate of soda and other salts 
which incrust the deserts of Utah, and often fill the air 
with alkaline dust, have accumulated in the same manner. 
So in our western caves the earth sheltered from rains is 
saturated with salts — epsom-salts, Glauber's-salts, and salt- 
peter, or mixtures of these. Often the rich soil of gardens 
is slightly incrusted in this manner in our summer weather ; 
but the saline matters are carried into the soil with the 
next rain. 

It is easy to see how, in a good soil, capillarity thus 
acts in keeping the roots of plants constantly immersed in 
a stream of water or moisture that is now ascending, now 
descending, but never at rest, and how the food of the 
plant is thus made to circulate around the organs fitted 
for absorbing it. 

The same causes that maintain this perpetual supj^ly of 
water and food to the plant are also efficacious in con- 
stantly preparing new supplies of food. As before ex- 
plained, the materials of the soil are always undergoing 
decomposition, whereby the silica, lime, phosphoric acid, 
potash, etc., of the insoluble fragments of rock, become 
soluble in water and accessible to the plant. Water 
charged with carbonic acid and oxygen is the chief agent 
in these chemical changes. The more extensive and rapid 
the circulation of water in the soil, the more matters Avill 
be rendered soluble in a given time, and, other things be- 
ing equal, the less will the soil be dependent on manures 
to keep up its fertility. 

Capacity of Imbibition. Capillary Power. — No mat- 
ter how favorable the structure of the soil may be to the 



180 HOW CROPS FEED. 

circulation of Avater in it, no continuous upward movement 
can take place without evaporation. The ease and rapid- 
ity of evaporation, while mainl}^ depending on the condi- 
tion of the atmosphere and on the sun's heat, are to a cer- 
tain degree influenced by the soil itself We have already 
seen that the soil possesses a power of absorbing watery 
vapor from the atmosphere, a power which is related both 
to the kind of material that forms the soil and to its state 
of division. This absorptive power oj^poses evaporation. 
Again, difierent soils manifest widely different capacities 
for imhibing liquid water — capacities mainly connected 
with their porosity. Obviously, too, the quantity of liquid 
in a given volume of soil affects not only the rapidity, 
but also the duration of evaporation. 

The following tables by Schiibler illustrate the peculi- 
arities of different soils in these respects. The first col- 
umn gives the percentages of liquid water absorbed by 
the completely dry soil. In these experiments the soils 
were thoroughly wet with water, the excess allowed to 
drip off*, and the increase of weight determined. In the 
second column are given the percentages of water that 
evaporated during the space of four hours from the satu- 
rated soil spread over a given surface : 

Quartz sand 25 88.4 

Gypsum 27 71.7 

Lirae sand 29 75.9 

Slaty mail 34 68.0 

Clay soil, (sixty per cent clay,) 40 52.0 

Loam 51 45.7 

Plough land 52 32.0 

Heavy clay, (eighty per cent clay,) 61 34.9 

Pure gray 'clay 70 31.9 

Fine carbonate of lime 85 28.0 

Garden mould 89 24.3 

Humus 181 25.5 

Fine carbonate of mairnesia 256 10.8 



It is obvious that these two columns express nearly the 
same thing in different ways. The amount of water re- 



1 



PERMEABILITY OF SOILS TO LIQUID WATER. 181 

tained increases from quartz sand to magnesia. The rap- 
idity of drying in the air diminishes in the same direction. 
Some observations of Zenger ( Wilda^s Centralblatty 
1858, 1, 430) indicate the influence of the state of division 
of a soil on its power of imbibing water. In the subjoin- 
ed table are given in the first cohimn the per cent of wa- 
ter imbibed by varioiis soils which had been brought to 
nearly the same degree of moderate fineness by sifting off 
both the coarse and the fine matter ; and the second col- 
umn gives the amounts imbibed by the same soils, reduced 
to a high state of division by pulverization. 





Coaj'se. 


Fine. 


Quartz sand, 


26.0 


53.5 


Marl (used as fertilizer,) 


30.3 


51.5 


Marl, underlying peat, 


39.0 


48.5 


Brick clay, 


66.2 


57.5 


Moor soil, 


104.5 


101.0 


Aim (lime-sinter,) 


108.3 


70.4 


Aim soil. 


178.2 


102.5 


Peat dust, 


377.0 


268.5 



The effects of pulverization on soils whose particles are 
compact is to increase the surface, and increase to a cor- 
responding degree the imbibing power. On soils consist- 
ing of porous particles, like lime-sinter and peat, pulver- 
ization destroys the porosity to some extent and diminishes 
the amount of absorption. The first class of soils are 
probably increased in bulk, the latter reduced, by grinding. 

Wilhelm, {Wilda's Centralblatt, 1866, 1, 118), in a 
series of experiments on various soils, confirms the above 
results of Zenger. He found, e. g., that a garden mould 
imbibed 114 per cent, but when pulverized absorbed but 
62 per cent. 

To illustrate the different properties of various soils for 
which the farmer has but one name, the fact may be ad- 
duced that while Schiibler, Zenger, and Wilhelm found 
the imbibing power of " clay " to range between 40 and 
TO per cent, Stoeckhardt examined a " clay " from Saxony 



182 HOW CROPS FEED 

that held 150 per cent of water. So the humus of Schiib- 
ler imbibed 181 per cent ; the peat of Zenger, 377 per cent ; 
while Wilhelm examined a very porous peat that took up 
519 per cent. These differences are dependent mainly on 
the mechanical texture or porosity of the material. 

The want of capillary retentive power for 'water in the 
case of coarse sand is undeniably one of the chief reasons 
of its unfruitfulness. The best soils possess a medium re- 
tentive power. In them, therefore, are best united the 
conditions for the regular distribution of the soil-water 
under all circumstances. In them this process is not hin- 
dered too much either by wet or dry weather. The re- 
taining power of humus is seen to be more than double 
that of clay. This result might appear at first sight to 
be in contradiction to ordinary observations, for we are 
accustomed to see water standing on the surface of clay 
but not on humus. It must be borne in mind that clay, 
from its imperviousness, holds water like a vessel, the wa- 
ter remaining apj^arent ; but humus retains it invisibly, 
its action being nearly like that of a sponge. 

One chief cause of the value of a layer of humus on 
the surface of the soil doubtless consists in this great re- 
taining power for water, and the success that has attended 
the practice of green manuring, as a means of renovating 
almost w'orthless shifting sands, is in a great degree to be 
attributed to this cause. The advantages of mulching are 
explained in the same way. 

Soils which are over-rich in humus, especially those of 
reclaimed peat-bogs, have some detrimental peculiarities 
deserving notice. Stoeckhardt {Wilda's Centralhlatt^ 
1858, 2, 22) examined the soil of a cultivated moor in 
Saxony, which, wdien moist, had an imbibing power of 
60-69" Iq. After being thoroughly dried, however, it lost 
its adhesiveness, and the imbibing powder fell to 26-30" 1^. 

It is observed in accordance with these data that such 
soils retain water late in spring ; and when they become 



CHANGES OF THE BULK OF THE SOIL. 183 

very dry in summer they are slow to take up water again, 
SO that rain-water stands on the surface for a considerable 
time without penetrating, and when, after some days, it 
is soaked up, it remains injuriously long. Light rains 
after drought do little immediate good to such soils, 
while heavy rains always render them too wet and cold, 
unless they are suitably ameliorated. The same' is true to 
a less degree of heavy, compact clays. 

§ '^• 

CHANGES OF THE BULK OF THE SOIL BY DRYING AND 
FROST. 

The Shrinking of Soils on Drying is a matter of no 
little practical importance. This shrinking is of course 
offset by an increase of bulk when the soil becomes wet. 
In variable weather we have therefore constant changes 
of volume occurring. 

Soils rich in humus experience these changes to the 
greatest degree. The surfaces of moors often rise and 
fall with the wet or dry season, through a space of sev- 
eral inches. In ordinary light soils, containing but little 
humus, no change of bulk is evident. Otherwise, it is in 
clay soils that shrinking is most perceptible ; since these 
soils only dry superficially, they do not appear to settle 
much, but become full of cracks and rifts. Heavy clays 
may lose one-tenth or more of their volume on drying, 
and since at the same time they harden about the rootlets 
wliich are imbedded in them, it is plain that these indis- 
pensable organs of the plant must thereby be ruptured 
during the protracted dry weather. Sand, on the other 
hand, does not change its bulk by wetting or drying, and 
when present to a considerable extent in the soil, its par- 
ticles, being interposed between those of the clay, prevent 
the adhesion of the latter, so that, although a sandy loam 
shrinks not inconsiderably on drying, yet the lines of sepa- 



184 now CROPS FEED. 

ration are vastly more numerous and less wide than in 
purer clays. Such a soil does not " cake," but remains 
friable and powdery. 

Marly soils (containing carbonate of lime) are especially 
prone to fall to a fine powder during drying, since the 
carbonate of lime, which, like sand, shrinks very little, is 
itself in a state of extreme division, and therefore more 
effectually separates the clayey particles. The unequal 
shrinking of these two intimately mixed ingredients ac- 
complishes a perfect pulverization of such soils. On the 
cold, heavy soils of Upper Lusatia, in Germany, the appli- 
cation of lime has been attended with excellent results, 
and the larger share of the benefit is to be accounted for 
by the improvement in the texture of those soils which 
follows liming. The carbonate of lime is considerably 
soluble in Avater charged with carbonic acid, as is the wa- 
ter of a soil containing vegetable matter, and this agency 
of distribution, in connection with the mechanical opera- 
tions of tillage, must in a short time effect an intimate 
mixture of the lime with the whole soil. A tenacious clay 
is thus by a heavy liming made to approach the condition 
of a friable marl. 

HcaTini^ by Frost. — Soils which imbibe much water, 
especially clay and peat soils, have likewise the disagree- 
able property of being heaved by frost. The expansion, 
by freezing, of the liquid water they contain, separates the 
particles of soil from each other, raises, in fact, the surface 
for a considerable height, and thus ruptures the roots of 
grass and especially of fall-sowed grain. The lifting of 
fence posts is due to the same cause. 



ADHESIVENESS OF THE SOIL. 

In Iho language of the farm a soil is said to be heavy 
or light, not as it weighs more or less, but as it is easy or 



ADHESIVENESS OP THE SOIL. 185 

difficult to work. The state of dryness has great influence 
on this quality. Sand, lime, and humus have very little 
adhesion when dry, but considerable when wet. Soils in 
which they predominate are usually easy to work. But 
clay or impalpable matter has entirely different characters, 
upon which the tenacity of a soil almost exclusively de- 
pends. Dry "clay," when powdered, has hardly more 
consistence than sand, but w^hen thoroughly moistened its 
particles adhere together to a soft and plastic, but tena- 
cious mass ; and in drymg away, at a certain point it be- 
comes very hard, and requires a good deal of force to 
penetrate it. In this condition it offers great resistance to 
the instruments used in tillage, and when thrown up by 
the plow it forms lumps which require repeated harrow- 
ings to break them down. Since the adhesiveness of the 
soil depends so greatly upon the quantity of water con- 
tained in it, it follows that thorough draining, combined 
with deep tillage, w^hereby sooner or later the stiffest clays 
become readily permeable to water, must have the best 
effects in making such soils easy to work. 

The English practice of burning clays speedily accom- 
plishes the same purpose. When clay is burned and then 
crushed, the particles no longer adhere tenaciously to- 
gether on moistening, and the mass does not acquire again 
the unctuous plasticity peculiar to unburned clay. 

Mixing sand with clay, or incorporating vegetable mat- 
ter vfith it, or liming, serves to separate the particles 
from each other, and thus remedies too great adhesiveness. 

The considerable expansion of water in the act of solid- 
ifying (one-fifteenth of its volume) has already been no- 
ticed as an agency in reducing rocks to powder. In the 
same way the alternate freezing and thawing of the water 
which impregnates the soil during the colder part of the 
year plays an important part in overcoming its adhesion. 
The effect is apparent in the spring, immediately after 
" the fi-ost leaves the ground," and is very considerable, 



186 HOW CROPS FEED. 

r 

fully one-third of the resistance of a clay or loam to the 
plow thus disappearing, according to Schiibler's experi- 
ments. 

Tillage, when carried on with the soil in a wet condi- 
tion, to some extent neutralizes the effects of frost, espe- 
cially in tenacious soils. 

Fall-jDlowing of stiff soils has been recommended, in 
order to expose them to the disintegrating effects of frost. 

§9- 

EELATIONS OF" THE SOIL TO HEAT. 

The relations of the soil to heat are of the utmost im- 
portance in affecting its fertility. The distribution of 
plants is, in general, determined by differences of mean 
temperature. In the same climate and locality, however, 
we find the farmer distinguishing between cold and warm 
soils. 

The Temperature of the Soil varies to a certain depth 
with that of the air ; yet its changes occur more slowly, 
are confined to a considerably narrower range, and dimin- 
ish downward in rapidity and amount, until at a certain 
depth a point is reached where the temperature is invari- 
able. 

In summer the temperature of the soil is higher in day- 
time than that of the air ; at night the temperature of the 
surface rapidly falls, especially when the sky is clear. 

In temperate climates, at a depth of three feet, the tem- 
perature remains unchanged from day to night ; at a depth 
of 20 feet the annual temperature varies but a degree or 
two ; at 75 feet below the surface, the thermometer re- 
mains perfectly stationary. In the vaults of the Paris 
Observatory, 80 feet deep, the temperature is 50° Fahren- 
heit. In tropical regions the point of nearly unvarying 
temperature is reached at a depth of one foot. 



RELATIONS OF THE SOIL TO HEAT. 187 

The mean annual temperature of the soil is the same as, 
or in higher latitudes a degree above, that of the air. The 
nature and position of the soil must considerably influence 
its temiDcrature 

Sources of the Heat of the Soil. — ^The sources of that 
heat which is found in the soil are three, viz. : First, the 
original heat of the earth ; second, the chemical process 
of oxidation or decay going on within it ; and third, an 
external one, the rays of the sun 

The earth has within itself a source of heat, which 
maintains its interior at a high temperature ; but which 
escapes so rapidly from the surface that the soil would be 
constantly frozen but for the external supply of heat from 
the sun. 

The heat evolved by the decay of organic matters is 
not inconsiderable in porous soils containing much vegeta- 
ble remains; but decay cannot proceed rapidly until the 
external temperature has reached a point favorable to 
vegetation, and therefore this source of heat probably has 
no appreciable efiect, one way or the other, on the welfare 
of the plant. The warmth of the soil, so far as it favors 
vegetable growth, appears then to depend exclusively on 
the heat of the sun. 

The direct rays of the sun are the immediate cause of 
the warmth of the earth's surface. The temperature of 
the soil near the surface changes progressively with the 
seasons ; but at a certain depth the loss from the interior 
and the gain from the sun compensate each other, and, as 
has been previously mentioned, the temperature remains 
unchanged throughout the year. 

Daily Changes of Temperature, — During the day the 
sun's heat reaches the earth directly, and is absorbed by 
the soil and the solid objects on its surface, and also by 
the air and water. But these different bodies, and also 
the different kinds of soil, have very different ability to 
absorb or become warmed by the sun's heat. Air and 



18S now CEOPS FEED. 

water arc almost incapable of being warmed by heat ap- 
plied above them. Through the air, heat radiates without 
being absorbed. Solid bodies which have dull and porous 
surfaces absorb heat most rapidly and abundantly. The 
soil and solid bodies become Avarmed according to their 
individual capacity, and from them the air receives the 
heat which warms it. From the moist surface of the soil 
goes on a rapid evaporation of water, which consumes * a 
large amount of heat, so that the temperature of the soil 
is not rapidly but gradually elevated. The ascent of wa- 
ter from the subsoil to supply the place of that evaporat- 
ed, goes on as before described. \Yhen the sun declines, 
the process diminishes in intensity, and when it sets, the 
reverse takes place. The heat that had accumulated on 



* When a piece of ice is placed in a vessel whose temperature is increasing, 
by means of a lamp, at the rate of one degree of the thermometer every minute, 
it will he found that the temperature of the ice rises until it attains 32'. AVheu 
this point is reached, it begins to melt, but doe« not suddenly become fluid : the 
melting goes on very gradually. A thermometer placed in the water remains 
constantly at 32° so long as a fragment of ice is present. The moment the ice 
disappears, the temperature begins to rise again, at the rate of one degree per 
minute. The time during which the temperature of the ice and water remains 
at 32° is 140 minutes. During each of these minutes one degree of heat enters 
the mixture, but is not indicated by the thermometer — the mercury remains sta- 
tionary ; 140° of heat liave thus passed into the ice and become hidden, latent ; 
at the same time the solid ice has become liquid water. The difference, then, 
between ice and water consists in the heat that is latent in the latter. If we now 
proceed Avith the above experiment, allowing the heat to increase with the same 
rapidity, we find that the temperature of the water rises constantly for ISO min- 
utes. The thermometer then indicates a temperature of 212°, (32+180,) and the 
water boils. Proceeding with the experiment, the water evaporates away, but 
the thermometer continues stationary so long as any liquid remains. After the 
lapse of 972 minutes, it is completely evaporated. Water in becoming steam 
renders, therefore, still another portion, 972°, of heat latent. The heat latent in 
steam is indispensable to the existence of the latter. If this heat be removed 
by bringing the steam into a cold space, water is reproduced. If, by means of 
pressure or cold, steam be condensed, the heat originally latent in it becomes 
sensible, //¥€, and capable of aff"ecting the thermometer. If, also, water be con- 
verted into ice, as much heat is evolved and made sensible as was absorbed and 
made latent. It is seen thus that the processes of liquefaction and vaporization 
are cooling processes ; for the heat rendered latent by them must be derived from 
surrounding objects, and thus these become cooled. On the contrary, solidifica- 
tion, freezing, and vapor-condensation, arc umrming processes, since in them 
large quantities of heat cease to be latent and arc made sensible, thus warming 
surrounding bodies. 



KELATIONS OF THE SOIL TO HEAT. 189 

the surface of the earth radiates into the cooler atmos- 
phere and planetary space ; the temperature of the surface 
rapidly diminishes, and the air itself becomes cooler by 
convection.* As the cooling goes on, the vapor suspend- 
ed in the atmosphere begins to condense upon cool objects, 
M'hile its latent heat becoming free hinders the too sudden 
reduction of temperature. The condensed water collects 
in drops — it is dew ; or in the colder seasons it crystallizes 
as hoar-frost. 

The deposition of liquid water takes place not on the 
surface of the soil merely, but within it, and to that dej^th 
in which the temperature falls during the night, viz., 12 
to 18 inches. (Krutzsch observed the temperature of a 
garden soil at the depth of one foot, to rise 3° F. on a 
May day, from 9 A. M. to 7 P. M.) 

Since the air contained in the interstices of the soil is at 
a little depth saturated with aqueous vapor, it results that 
the slightest reduction of temperature must at once occa- 
sion a deposition of water, so that the soil is thus supplied 
wdth moisture independently of its hygroscopic power. 

Conditions that Affect the Temperature of the Soil. — 
The special nature of the soil is closely connected with 
the maintenance of a uniform temperature, wdth the pre- 
vention of too great heat by day and cold by night, and 
with the watering of vegetation by means of dew. It is, 
however, in many cases only for a little space after seed- 
time that the soil is greatly concerned in these processes. 
So soon as it becomes covered with vegetation, the char- 



* Though liquids and gases ai*e almost perfect non-conductors of heat, yet it can 
diffuse through them rapidly, if advantage be taken of the fact that by heating they 
expand and therefore become specifically lighter. If heat be applied to the upper 
surface of liquids or gases, they remain for a long time nearly unaffected ; if 
it be applied bemath them, the lower layers of particles become heated and rise, 
their place is supplied by others, and so currents upward and downward are 
established, whereby the heat is rapidly and uniformly distributed. This process 
of convection can rarely have any influence in the soil. What we have stated 
concerning it shows, however, in what way the atmosphere may constantly act 
in removing heat from the surface of the soil. 



190 now CKOPS FEED. 

acter of the latter determines to a certain degi-ee the na- 
ture of the atmosplieric changes. In case of many crops, 
the soil is but partially covered, and its peculiarities are 
then of direct influence on its temperature. 

Relation of Temperature to Color and Texture.— It 
is usually stated tliat black or dark-colored soils are sooner 
warmed by the sun's rays than those of lighter color, and 
remain constantly of a higher temperature so long as the 
sun acts on them. An elevation of several degrees in the 
temperature of a light-colored soil may be caused by 
strewing its surface with peat, charcoal powder, or vege- 
table mould. To this influence may be partly ascribed 
the following facts. Lampadius was able to ripen melons, 
even in the coolest summers, in Freiberg, Saxony, by 
strewing a coating of coal dust an inch deep over the sur- 
face of the soil. In Belgium and on the Rhine, it is found 
that the grape matures best, when the soil is covered with 
fragments of black clay slate. 

According to Creuze-Latouche, the vineyards along the 
river Loire grow either upon a light-colored calcareous 
soil, or upon a dark red earth. These two kinds of soil 
often alternate with each other within a little distance, 
and the character of the wine produced on them is remark- 
ably connected with the color of the earth. On the light- 
colored soils only a weak, white wine can be raised to ad- 
vanta2i:e, while on conti<?uous dark soils a strons: claret of 
fine quality is made. (Gasparin, Cours cV Agriculture^ 1, 
103.) 

Girardin found in a series of exj)eriments on the cultiva- 
tion of 2)otatoes, tliat the time of their ripening varied 
eight to fourteen days, according to the color of the soil. 
He found on August 25th, in a very dark humus soil, 
twenty-six varieties ripe ; in sandy soil, twenty ; in clay, 
nineteen ; and in white lime soil, only sixteen. It is not 
difficult, however, to indicate other causes that will ac- 
count in part for the results of Girardin. 



RELATIONS OF THE SOIL TO HEAT. 191 

Schiibler made observations on the temperatures at- 
tained by various dry soils exposed to the sun's rays, 
according as their surfaces were blackened by a thin 
sprinkling of lamp-black or whitened by magnesia. His 
results are given in columns 1 and 2 of the following table 
(vide p. 196,) from which it is seen that the dark surface 
was warmed 13° to 14° more than the white. We like- 
wise notice that the character of the v^ery surface deter- 
mines the degree of Avarmth, for, under a sprinkling of 
lamp-black or magnesia, all the soils experimented with 
became as good as identical in their absorbing poAver for 
the Sim's heat. 

The observations of Malaguti and Durocher prove that 
the peculiar temperature of the soil is not always so 
closely related to color as to other qualities. They studied 
the thermometric characters of the following soils, viz. : 
Garden earth of dark gray color, — a mixture of sand and 
gravel with about five per cent of humus ; a grayish- 
white quartz sand ; a grayish-brown granite sand ; a fine 
light-gray clay (pipe clay) ; a yellow sandy clay ; and, 
finally, four lime soils of different physical qualities. 

It was found that when the exposure was alike, the 
dark-gray granite sand became the warmest, and next to 
this the grayish- white quartz sand. The latter, notwith- 
standing its lighter color, often acquired a lygher temjjer- 
ature at a depth of four inches than the former, a fact to 
be ascribed to its better conducting power. The black 
soils never became so warm as the two just mentioned. 
After the black soils, the others came in the following or- 
der : garden soil ; yellow sandy clay ; pipe clay ; lime 
soils having crystalline grains ; and, lastly, a j^ulverulent 
chalk soil. 

To show what different degrees of warmth soils may 
acquire, under the same circumstances, the following max- 
imum temperatures may be adduced : At noon of a July 
day, when the temperature of the air was 90°, a thermom- 



192 HOW CROPS FEED. 

eter placed at a depth of a little more than one inch, gave 

these results : 

In quartz sand 136° 

In crystalline lime soil 115° 

In garden soil 114° 

In yellow sandy clay 100° 

In pipe clay 94° 

In chalk soil 87* 

Here we observe a difference of nearly 40° in the noon- 
day temperature of the coarse quartz and the chalk soil. 
Malaguti and Durocher found that the temperature of the 
garden soil, just below the surface, w^as, on the average 
of day and night together, G° Fahrenheit higher than that 
of the air, but that this higher temperature diminished at 
a greater depth. A thermometer buried four inches indi- 
cated a mean temperature only 3° above that of the at- 
mosphere. 

The experimenters do not mention the influence of wa- 
ter in affecting these results ; they do not state the degree 
of dryness of these soils. It will be seen, however, that 
the warmest soils are those that retain least water, and 
doubtless something of the slowness with which the fine 
soils increase in warmth is connected with the fact that 
they retain much water, which, in CA^aporating, appropri- 
ates and renders latent a large quantity of heat. 

The chalk ,soil is seen to be the coolest of all, its tem- 
perature in these observations being three degrees lower 
than that of the atmosphere at noonday. In hot climates 
this coolness is sometimes of great advantage, as appears 
to happen in Spain, near Cadiz, where the Sherry vine- 
yards flourish. " The Don said the Sherry wine district 
was very small, not more than twelve miles square. The 
Sherry grape grew only on certain low^, chalky hills, where 
the earth being light-colored, is not so much burnt ; did 
not chap and split so much by the sun as darker and 
heavier soils do. A mile beyond these hills the grape de- 
teriorates."— (Dickens' Household Words.^oY. 13,1858.) 



RELATIONS OF THE SOIL TO HEAT. 193 

In Explanation of these observations we must recall to 
mind the fact that all bodies are capable of absorbing and 
radiating as well as reflecting heat. These j^roperties, al- 
though never dissociated from color, are not necessarily- 
dependent upon it. They chiefly depend upon the char- 
acter of the surface of bodies. Smooth, polished surfaces 
absorb and radiate heat least readily ; they reflect it most 
perfectly. Radiation and absorption are opposed to each 
other, and tlie power of any body to radiate, is precisely 
equal to its faculty of absorbing heat. 

It must be understood, however, that bodies may diff"er 
in their power of absorbing or radiating heat of differeyit 
degrees of intensity. Lamp-black absorbs and radiates 
heat of all intensities in the same degree. Whitp-lead 
absorbs heat of low intensity (such as radiates from a ves- 
sel filled with boiling water) as fully as lamp-black, but 
of the intense heat of a lamp it absorbs only about one- 
half as much. Snow seems to resemble white-lead in this 
respect. If a black cloth or black paper be spread on the 
surface of snow, upon which the sun is shining, it will 
melt much faster under the cloth than elsewhere, and this, 
too, if the cloth be not in contact with, but susj^ended 
above, the snow. In our latitude every one has had op- 
portunity to observe that snow thaws most rapidly when 
covered by or lying on black earth. The people of Cham- 
ouni, in the Swiss Alps, strew the surface of their fields 
with black-slate powder to hasten the melting of the snow. 
The reason is that snow absorbs heat of low intensity 
with greatest facility. The heat of the sun is converted 
from a high to a low intensity by being absorbed and then 
radiated by the black material. But it is not color that 
determines this diflerence of absorptive power, for indigo 
and Prussian blue, though of nearly the same color, have 
very diflferent absorptive powers. So far, however, as our 
observations extend, it appears that, usually, dark-colored 
soils absorb heat most rapidly, and that the sun's rays 
9 



194 HOW CROPS FEED. 

have least effect on light-colored soils. (See the table on 
p. 196.) 

The Rapidity of Change of Temperature independently 
of color or moisture has been determined on a number of 
soils by Schtibler. A given volume of dry soil was heat- 
ed to 145°, a thermometer was placed in it, and the time 
was observed which it required to cool down to 70°, the 
temperature of the atmosphere being 61°. The subjoined 
table gives his results. In one column are stated the 
times of cooling, in another the relative power of retaining 
heat or capacity for heat, that of lime sand being assumed 
as 100. 

Lime sand 3 hours 

Quartz sand 3 " 

Potter's clay . . . : 2 " 

Gypsum 2 " 

ciay loam 2 " 

Clay plow land 2 " 

Heavy cla}'' 2 " 

Pure iii-ay clay 2 " 

Garden earth 2 " 

Fine carb. Ihne 2 " 

Humus 1 " 

Magnesia 1 " 

It is seen that the sandy soils cool most slowly, then 
follow clays and heavy soils, and lastly comes humus. 

The order of cooling above given is in all respects 
identical with that of warming, provided the circumstances 
are alike. In other words these soils, containing no moist- 
ure, or but little, and exposed to heat of low intensity, 
would be raised through a given range of temj^erature in 
the same relative times that they fall through a given 
number of degrees. 

! It is to be particularly noticed that dark humus and white 
magnesia are very closely alike in their rate of cooling, 
and cool rapidly ; while white lime sand stands at the op- 
l^osite extreme, requiring twice as long to cool to the same 
extent. These facts strikingly illustrate the great differ- 



30min... 


...100 


27 ".... 


95.6 


41 *'.... 


76.9 


34 ".... 


....73.8 


30 ".... 


71.8 


27 "..., 


70.1 


24 ".... 


....68.4 


19 ".... 


....66.7 


16 ".... 


....64.8 


10 ".... 


....61.3 


43 ".... 


....49.0 


20 ".... 


....38.0 



RELATIONS OP THE SOIL TO HEAT. 195 

ence between the absorption of radiant heat of low inten- 
sity or itsjcommunication by conduction on one hand, and 
that of high intensity like the heat of the sun on the other. 

Retention of Heat. — Other circumstances being equal, 
the power of retaining heat (slowness of cooling) is the 
greater, the greater the weight of a given bulk of soil, 
i. e., the larger and denser its particles. 

A soil covered with gravel cools much more slowly 
than a sandy surface, and the heat which it collects during a 
sunny day it carries farther into the night ; hence gravelly 
soils are adapted for such crops as are liable to fail of rip- 
ening in cool situations, especially grapes, as has been 
abundantly observed in practice. 

Color is without influence on the loss of heat from the 
soil by radiation, because the heat is of low intensity. 
The porosity or roughness of the surface (extent of sur- 
face) determines cooling from this cause. Dew, which is 
deposited as the result of cooling by radiation of heat into 
the sky, forms abundantly on grass and growing vege- 
tation, and on vegetable mould, but is more rarely met with 
on coarse sand or gravel. 

Influence of Moisture on the Temperature of the Soil. 
— ^All soils, when thoroughly wet, seem to be nearly alike 
in their power of absorbing and retaining warmth. This 
is due to the fact that the capacity of water for heat is 
much greater than that of the soil. We have seen that 
lime sand and quartz sand are the slowest of all the in- 
gredients of soils to suffer changes of temperature when 
exposed to a given source of heat. (See table, p. 194.) 

Now, water is nine times slower than quartz in being 
affected by changes of temperature, and as the entire sur- 
face of the wet soil is water, which is, besides, a nearly 
perfect non-conductor of heat, we can understand that ex- 
ternal warmth must affect it slowly. 

Again, the immense consumption of heat in theforma- 
tiqn of vapor (see note, p. 188) must prevent the wet soil 



196 



HOAV CROPS FEED. 



from ever acquiring the temperature it shortly attains 
when dry. 

From this cause the difference in temperature between 
dry and wet soil may often amount to from 1*0° to 18°. 

On this point, again, Schiibler furnishes us with the re- 
sults of his experiments. Columns 4 and 5 in the table 
below give the temperatures which the thermometer at- 
tained Avhen its bulb was immersed in various soils, both 
wet and dry, each having its natural color. (Columns 1 
and 2 are referred to on p. 191.) 



Magnesia, pure white 

Fine carbonate of lime, Avhite 

Gypsum, bright white-gray 

Plow land, gray 

Sandy clay, yellowish 

Quartz sand, bright yellowish-gray. 

Loam, yellowish 

Lime sand, Avhitish-gray 

Heavy clay soil, yellowish-gray 

Pure clay, blnish-gray 

Garden monld, blackish-gray 

Slaty marl, brownish-red 

Humus, brownish-black 



12 3 

Surface. 



Whit- Black- 
ened, ened. 



108.7' 
109.2' 
110.3' 
107.6' 
108.3' 
109.9' 
107.8= 
109.9' 
107.4' 
106.3' 
108.8' 
108.8' 
108.5' 



121.8 
122.9 
124.3° 
122.0° 
121.0° 
123.6° 
121.1° 
124.0° 
120.4° 
120.0° 
122.5° 
123.4° 
120.9° 



Differ- 
ence. 



12.6° 
13.7° 
14.0° 
14.4° 
13.8° 
13.7° 
13.3° 
14.1° 
13.0° 
18.7° 
14.2° 
15.1° 
12.4° 



4 5 

Surface. 



Wet. Dry. 



95.2° 
96.1 
97.3° 
97.7° 
98.2° 
99.1° 
99.1° 
99.8° 
99.8° 
99.5° 
99.5° 
101.8° 
103.6° 



108.7° 
109.4° 
110.5° 
111.7° 
111.4° 
112.6° 
112.1° 
112.1° 
112.3° 
113.0° 
113.5° 
115.3° 
117.3° 



Differ- 
ence. 



13.5° 
13.3° 
13.2° 
14.0° 
13.2° 
13.5° 
18.0' 
12.8° 
18.0° 
18.5° 
14.0° 
18.5° 
13.7° 



We note that the difference in favor of the dry earth is 
almost uniformly 13° to 14°. This difference is the same 
as observed between the whitened and blackened speci- 
mens of the same soils. (Column 3.) 

We observe, however, that the wet soil in no case be- 
comes as warm as the same soil whitened. We notice 
further that of the wet soils, the dark-colored ones, humus 
and marl, are most highly heated. Further it is seen that 
coarse lime sand (carbonate of lime) acquires 3° higher 
I temperature than fine carbonate of lime, both wet, j^rob- 
ably because evaporation proceeded more slowly from the 
coarse than from the fine materials. Again it is plain on 
comparing columns 1, 2, and 5, that the gray to yellowish 
brown and black colors of all the soils, save the first three, 
assist the elevation of temperature, which rises nearly 



RELATIONS OF THE SOIL TO HEAT. 197 

with the deepening of the color, until in case of humus it 
lacks but a few degrees of reaching the warmth of a sur- 
face of lamp-black. 

According to the observations of Dickinson, made at 
Abbot's Hill, Hertfordshire, England, and continued 
through eight years, 90 per cent of the water falling be- 
tween April 1st and October 1st evaporates from the sur- 
face of the soil, only 10 per cent finding its way into 
drains laid three and four feet deep. The total quantity 
of water that fell during this time amounted to about 
2,900,000 lbs. per acre; of this more than 2,600,000 evap- 
orated from the surface. It has been calculated that to 
evaporate artificially this enormous mass of water, more 
than seventy-five tons of coal must be consumed. 

Thorough draining, by loosening the soil and causing a 
rapid removal from below of the surplus water, has a most 
decided influence, especially in spring time, in warming 
the soil and bringing it into a* suitable condition for the 
support of vegetation. 

It is plain, then, that even if we knew with accuracy 
what are the physical characters of a surface soil, and if 
we were able to estimate correctly the influence of these 
characters on its fertility, still we must investigate those 
circumstances which affect its wetness or dryness, whether 
they be an impervious subsoil, or springs coming to the 
surface, or the amount and frequency of rain-falls, taken 
in connection with other meteorological causes. We can- 
not decide that a clay is too wet or a sand too dry, until 
we know its situation and the climate it is subjected to. 

The great deserts of the globe do not owe their barren- 
ness to necessary poverty of soil, but to meteorological 
influences — to the continued prevalence of parcbing winds, 
and the absence of mountains, to condense the atmospheric 
water and establish a system of rivers and streams. This 
is not the place to enter into a discussion of the causes 
that may determine or modify climate ; but to illustrate 



198 HOW CROPS FEED. 

the effect that may be produced by means within human 
control, it may be stated that previous to the year 1821, 
the French district Provence was a fertile and well-water- 
ed region. In 1822, the olive trees which were largely 
cultivated there were injured by frost, and the inhabitants 
began to cut them up root and branch. This amounted 
to clearing off a forest,, and, in consequence, the streams 
dried up, and the productiveness of the country was seri- 
ously diminished. 

The Angle at which the Sun's Rays Strike a Soil is 

of great influence on its temperature. The more this ap- 
proaches a right angle the greater the heating effect. In 
the latitude of England the sun's heat acts most power- 
fully on surfaces having a southern exposure, and which 
are inclined at an angle of 25° and 30°. The best vine- 
yards of the Rhine and Neckar are also on hill-sides, so 
situated. In Lapland and Spitzbergen the southern 
side of hills may be seen covered with vegetation, while 
lasting or even perpetual snow lies on their northern in- 
clinations. 

The Inflaence of a Wall or other Reflecting Surface 

upon the warmth of a soil lying to the south of it was 
observed in the case of garden soil by Malaguti and 
Durocher. The highest temperature indicated by a ther- 
mometer placed in this soil at a distance of six inches from 
the wall, during a series of observations lasting seven days 
(April, 1852), was 32° Fahrenheit higher at the surface, 
and 18° higher at a depth of four inches than in the same 
soil on the north side of the wall. The average temper- 
ature of the former during this time was 8° higher than 
that of the latter. In another trial in March the difference 
in average temperature between the southern and north- 
ern exposures was nearly double this amount in favor of 
the former. 

As is well known, fruits which refuse to ripen in cold 
climates under ordinary conditions of exposure may attain 



THE FREE AVATER OF THE SOIL. 199 

perfection when trained against the sunny side of a wall. 
It is thus that in the north of England pears and plums 
are raised in the most unfavorable seasons, and that the 
vineyards of Fontainebleau produce such delicious Chas- 
selas grapes for the Paris market, the vines being trained 
against walls on the Thomery system. 

In the Khine district grape vines are kept low and as 
near the soil as possible, so that the heat of the sun may be 
reflected back upon them from the ground, and the ripen- 
ing is then carried through the nights by the heat radiated 
from the earth. — {Journal Highland and Agricultural 
Society, July, 1858, p. 347.) 

Vegetation. — Malaguti and Durocher also studied the 
effect of a sod on the temperature of the soil. They ob- 
served that it hindered the warming of the soil, and in- 
deed to about the same extent as a layer of earth of three 
inches depth. Thus a thermometer four inches deep in 
green-sward acquires the same temperature as one seven 
inches deep in the same soil not grassed. 



CHAPTER V. 

THE SOIL AS A SOURCE OF FOOD TO CROPS.— 

INGREDIENTS WHOSE ELEMENTS ARE OF 

ATMOSPHERIC ORIGIN. 

§ 1- 

THE FREE WATER OF THE SOIL IN ITS RELATIONS TO 
VEGETABLE NUTRITION. 

Water may exist free in the soil in three conditions, 
which we designate respectively hydrostatic, capillary, 
and hygroscopic. 

Hydrostatic or Flowing * Water is water visible as 



* I. e., capable of flowing. 



200 now CKOPs feed. 

such to the eye, and free to obey the laws of gravity and 
motion. When the soil is saturated by rains, melting 
snows, or by overflow of streams, its pores contain hy- 
drostatic Avater, which sooner or later sinks away into the 
subsoil or escapes into drains, streams, or lower situations. 

Bottom Water is permanent hydrostatic water ^ reached 
nearly always in excavating deep soils. The surface of 
water in a well corresponds with, or is somewhat below, the 
upper limit of bottom water. It usually fluctuates in 
level, rising nearer the surface of the soil in wet seasons, 
and receding during drought. In general, agricultural 
plaiits are injured if their roots be immersed for any length 
of time in hydrostatic water ; and soils in which bottom 
water is found at a little depth during the season of 
growth arc unprofitable for culture. 

If this depth be but a few inches, we have a bog, 
swamp, or swale. If it is one and a half to three feet, 
and the surface soil be light, gravelly, or open, so as to 
admit of rapid evaporation, some plants, especially grasses, 
may flourish. If at a constant depth of four to eight feet 
under a gravelly or light loamy soil, it is favorable to 
crops as an abundant source of water. 

Heavy clays, which retain hydrostatic water for a long 
time, being but little j^ermeable, are for the same reasons 
unfavorable to most crops, unless artificial provision be 
made for removing the excess. 

Rice, as Ave have seen, (H. C. G., p. 252), is a plant 
which grows well with its roots situated in water. Hen- 
ri ci's experiment with the raspberry (H. C. G., p. 254), 
and the frequent finding of roots of clover, turnips, etc., 
in cisterns or drain pipes, indicate that many or all 
agricultural plants may send down roots into the bottom 
Avater for the purpose of gathering a sufficient supply of 
this necessary liquid. 

Capillary Water is that Avhich is held in the fine pores 
of the soil by the surface attraction of its particles, as oil 



THE FEEE AVATEU OF THE SOIL. 201 

is held in the wick of a lamp. The adhesion of the water 
to the particles of earth suspends the flow of the liquid, 
and it is no longer subject to the laws of hydrostatics. 
Capillary water is usually designated as moisture, though 
a soil saturated with capillary water would be, in most 
cases, wet. The capillary power of various soils has al- 
ready been noticed, and is for coarse sands 25° |„; for 
loams and clays, 40 to 70°!^; for garden mould and humus, 
much higher, 90 to 300 ° |„. (See p. 180.) 

For a certain distance above bottom water, the soil is 
saturated with capillary water, and this distance is the 
greater, the greater the capillary power of the soil, i. e., 
the finer its pores. 

Capillary water is not visible as a distinct liquid layer 
on or between the particles of soil, but is still recogniza- 
ble by the eye. Even in the driest weather and in the 
driest sand (that is, when not shut off from bottom water 
by too great distance or an intervening gravelly subsoil) it 
may be found one or a few inches below the surface where 
the soil looJcs moist — has a darker shade of color. 

Hygroscopic Water is that which is not perceptible to 
the senses, but is appreciated by loss or gain of weight in 
the body which acquires or is deprived of it. (H. C. G., 
p. 54.) The loss experienced by an air-dry soil when kept 
for some hours at, or slightly above, the boiling point 
(212° F.,) expresses its content of hygroscopic water. 
This quantity is variable according to the character of the 
soil, and is constantly varying with the temperature ; in- 
creasing during the night when it is collected from the at- 
mosphere, and diminishing during the day when it returns 
in part to the air. (Se^p. 164.) The amount of hygros- 
copic water ranges from 0.5 to 10 or more per cent. 

Value of these Distinctions. — These distinctions be- 
tween hydrostatic, capillary, and hygroscopic water, are 
nothing absolute, but rather those of degree. Hygroscopic 
water is capillary in all respects, save that its quantity is 



202 HOW CROPS FEED. 

small, and its adhesion to the particles of soil more firm 
for that reason. Again, no precise boundary can always 
be drawn between capillary and hydrostatic water, espe- 
cially in soil having fine pores. The terms are neverthe- 
less useful in conveying an idea of the degrees of wet- 
ness or moisture in the soil. 

Roots Absorb Capillary or Hygroscopic Water.— It is 

from capillary or hygroscopic water that the roots of most 
agricultural plants chiefly draw a supply of this liquid, 
though not infrequently they send roots into wells and 
drains. The physical characters of soils that have been 
already considered suffice to explain how the earth acquires 
this water ; it here remains to notice how the plant is re- 
lated to it. 

As we have seen (pp. 35-38), the aerial organs appear 
incapable of taking up either vapor or liquid water from 
the air to much extent, and even roots continually exhale 
vapor without absorbing any, or at least without being able 
to make up the loss which they continually sufier. 

Transpiration of Water through Plants. — It is a most 
familiar fact that water constantly exhales from the surface 
of the plant. The amount of this exhalation is often very 
great. Hales, the earliest observer of this phenomenon, 
found that a sunflower whose foliage had 39 square feet 
of surface, gave off in 24 hours 3 lbs. of w^ater. A cab- 
bage, whose surface of leaves equaled 19 square feet, ex- 
haled in the same time very nearly as much. Schleiden 
found the loss of water from a square foot of grass-sod to 
be more than l| lbs. in 24 hours. Schtibler states that in 
the same time 1 square foot of pasture-grass exhaled 
nearly 5^ lbs. of water. In one*of Knop's more recent 
experiments, {Vs. jSt., VI, 239), a dwarf bean exhaled 
during 23 days, in September and October, 13 times its 
weight of water. In another trial a maize-plant transpir- 
ed 36 times its weight of water, from May 22d to Sept. 
4th. According to Knoj), a grass-plant will exhale its own 



THE FREE WATER OF THE SOIL. 203 

weight of water in 24 hours of hot and dry summer 
weather. 

The*water exhaled from the leaves must be constantly 
suppHed by absorption at the roots, else the foliage soon 
becomes flabby or wilts, and finally dies. Except so far 
as water is actually formed or fixed within the plant, its 
absorption at the roots, its passage through the tissues, 
and its exhalation from the foliage, are nearly equal in 
quantity and mutually dependent during the healthy ex- 
istence of vegetation. 

Circumstances that Influence Transpiration.— c^ TJie 
structure of the leaf including the character of the epi- 
dermis, and the number of stomata as they afiect exhala- 
tion, has been considered in " How Crops Grow," (pp. 
286-8). 

h. The physical conditions which facilitate evapora- 
tion increase the amount of water that passes through 
the plant. Exhalation of water-vapor j^roceeds most 
rapidly in a hot, dry, windy summer day. It is nearly 
checked when the air is saturated with moisture, and va- 
ries through a wide range according to the conditions just 
named. 

c. The oxidations that are constantly going on within 
the plant may, under certain conditions, acquire sufficient 
intensity to develop a perceptible amount of heat and 
cause the vaporization of water. It has been repeatedly 
noticed that the process of flowering is accompanied by 
considerable elevation of temperature, (p. 24). In general, 
however, the opposite j^rocess of deoxidation i^reponder- 
ates with the plant, and this must occasion a reduction of 
temperature. These interior changes can have no apprecia- 
ble influence upon transpiration as compared with those 
that depend upon external causes. Sachs, found in some 
of his experiments (p. 36) that exhalation took place from 
plants confined in a limited space over water. Sachs be- 



204 HOW CROPS FEED. 

lieved that the air suiToiindmg the plants in these experi- 
ments was saturated Avith vapor of Avater, and conchided 
that heat was develoj^ed within the plant, which caused 
vaporization. More recently, Boehm {Sitzungsberichte 
der Wienej" A7cad., XLYIII, 15) has made probable that 
the air was not fully or constantly saturated with moist- 
ure in these experiments, and by taking greater precau- 
tions has arrived at the conclusion that transpiration abso- 
lutely ceases in air saturated with aqueous vapor. 

d. The condition of the tissues of the plant, as depend- 
ent upon their age and vegetative activity, likewise has a 
marked effect on transpiration. Lawes * and Knop both 
found that young plants lose more water than older ones. 
This is due to the diminished power of mature foliage to 
imbibe and contain water, its cells becoming choked up 
with growth and inactive. 

e. TJie character of the medium in lohich the roots are 
situated also remarkably influences the rate of transpira- 
tion. This fact, first observed by Mr. Lawes, in 1850, loo. 
cit., was more distinctly brought out by Dr. Sachs at a 
later period. ( Vs. jSt., I, p. 203.) 

Sachs experimented on various plants, viz. : beans, 
squashes, tobacco, and maize, and observed their transpi- 
ration in weak solutions (mostly containing one per cent) 
of nitre, common salt, gypsum, (one-fifth i^er cent solu- 
tion) and sulphate of ammonia. He also experimented 
with maize in a mixed solution of phosphate and silicate 
of potash, sulphates of lime and magnesia, and common 
salt, and likewise observed the effect of free nitric acid 
and free potash on the squash plant. The young plants 
were either germinated in the soil, then removed from it 
and set with their rootlets in the solution, or else were 
kept in the soil and watered with the solution. The glass 



* ExperinientaZ Investigation into the Amount of Water given off hrj Plants 
during their Growth, by J, B. Lawes, of Rothamstead, London, 1850. 



THE FREE WATER OF THE SOIL. 205 

vessel containing the plant and solution was closed above, 
around the stem of the plant, by glass plates and cement, 
so that no loss of water could occur except through the 
plant itself, and this loss was ascertained by daily weigh- 
ings. The result Avas that all the solutions mentioned, 
except that of free nitric acid, quite uniformly retarded 
transpiration to a degree varying from 10 to 90 per cent, 
while the free acid accelerated the transpiration in a cor- 
responding manner. 

Sachs experimented also with four tobacco plants, two 
situated in coarse sand and two in yellow loam. The 
plants stood side by side exposed to the same temperature, 
etc., and daily weighings were made during a week or 
more, to learn the amount of exhalation. The result was 
that the total loss, as well as the daily loss in the majority 
of weighings, was greater from the plant growing in loam, 
although through certain short periods the oj^posite was 
noticed. 

f. Tlie temperature of the soil considerably aifects the 
rate of transpiration by influencing the amount of absorp- 
tion at the roots. Sachs made a number of Aveighings up- 
on two tobacco plants of equal size, potted in portions of 
the same soil and having their foliage exposed to the same 
atmosphere. After observing their relative transpiration 
when their roots were at the same temperature, one pot 
was warmed a number of degrees, and the result was in- 
variably observed that elevating the temperature of the 
soil increased the transpiration. 

The same observer subsequently noticed the entire sup- 
pression of absorption by a reduction of temperature to 
41° to 43° F. A number of healthy tobacco and squash 
plants, rooted in a soil kept nearly saturated with water, ' 
were growing late in November in a room, the tempera- 
ture of which fell at night to the point just named. In 
the morning the leaves of these plants were so wilted 
that they hung down like wet cloths, as if the soil were 



306 HOW CKOPS FEED. 

completely dry, or they had been for a long time acted 
upon by a powerful sun. Since, however, the soil was 
moist, the wilting could only arise from the inability of 
the roots to absorb water as rapidly as it exhaled from 
the leaves, owing to the low temperature. Further ex- 
periments showed that warming the soil in which the 
wilted i^lants stood, restored the foliage to its proper tur- 
gidity in a short time, and by surrounding the soil of a 
fresh plant with snow, the leaves wilted in three or four 
hours. 

Cabbages, winter colza, and beans, similarly circum- 
stanced, did not wilt, showing that different plants are un- 
equally affected. The general rule nevertheless appears to 
be established that within certain limits the root absorbs 
more vigorously at high than at low temperatures. 

The Amount of Loss of Water of Vei^etatioii in Wilt- 
ing has been determined by Hesse ( Vs. St., I, 248) in 
case of sugar-beet leaves. Of two similar leaves, one, 
gathered at evening after several days of dryness and sun- 
shine, contained 85.74" 1^ of water; the other, gathered 
the next morning, two hours after a rain storm, yielded 
89.57° |„. The difference was accordingly 3.8°!,. Other 
observations corroborated this result. 

Is Exhalation Indispensable to Plants] — ^It was for 

a long time supposed that transpiration is indispensable 
to the life of plants. It was taught that the water which 
the j^lant imbibes from the soil to replace that lost by ex- 
halation, is the means of bringing into its roots the min- 
eral and other soluble substances that serve for its nutri- 
ment. 

There are, however, strong groimds for believing that 
the current of water which ascends through a plant moves 
independently of the matters that may be in solution, 
either without or within it ; and, moreoA^er, the motion of 
soluble matters from the soil into the plant may go on, 



THE FREE WATER OF THE SOIL. 207 

although there be no ascending aqueous current. (H. C. 
G., pp. 288 and 340.) 

In accordance with these views, vegetation grows as well 
in the confined atmosphere of green-houses or of Wardian 
Cases, where the air is for the most part or entirely satu- 
rated with vapor, so that transpiration is reduced to a mini- 
mum, as in the free air, where it may attain a maximum. 
As is well known, the growth of field crops and garden 
vegetables is often most rapid during damp and showery 
weather, when the transpiration must j^roceed with com- 
parative slowness. 

While the above considerations, together with the asser- 
tion of Knop, that leaves lose for the first half hour nearly 
the same quantities of water under similar exposure, 
whether they are attached to the stem or removed from 
it, whether entire or in fragments, would lead to the con- 
clusion that transpiration, which is so extremely variable 
in its amount, is, so to speak, an accident to the plant and 
not a process essential to its existence or welfare, there 
are, on the other hand, facts Avhich appear to indicate the 
contrary. 

In certain experiments of Sachs, in which the roots of 
a bean were situated in an atmosphere nearly saturated 
with aqueous vapor, the foliage being exposed to the air, 
although the plant continued for two months fresh and 
healthy to appearance, it remained entirely stationary in 
its development. ( Vs. /St., I, 237.) 

Knop also mentions incidentally ( Vs. St., I, 192) that 
beans, lupines, and maize, die when the whole plant is 
kept confined in a vessel over water. 

It is not, however, improbable that the cessation of 
growth in the one case and the death of the plants in the 
other were due not so much to the checking of transpira- 
tion, which, as we have seen, is never entirely suppressed 
under these circumstances, as to the exhaustion of oxygen 
or the undue accumulation of carbonic acid in the narrow 



208 HOW CROPS FEED. 

and confined atmosphere in which these results Avere 
noticed. 

On the whole, then, we conclude from the evidence be- 
fore us that transpiration is not necessary to vegetation, 
or at least fulfills no very important oflices in the nutrition 
of plants. 

The entrance of water into the plant and the steady 
maintenance of its proper content of tliis substance, under 
all circumstances is of the utmost moment, and leads us 
to notice in the next place the 

Direct Proof that Crops can Absorb from the Soil 
enough Hygroscopic Water to Maintain their LifCt— Sachs 
sufiered a young bean-plant standing in a jDot of very reten- 
tive (clay) soil to remain without watering until the leaves 
began to wilt. A high and spacious glass cylinder, having 
a layer of water at its bottom, was then provided, and the 
pot containing the wilting plant was supported in it, near 
its top, while the cylinder was capped by two semicircular 
plates of glass which closed snugly about the stem of the 
bean. The pot of soil and the roots of the plant were 
thus enclosed in an atmosphere which was constantly sat- 
urated, or nearly so, with watery vapor, while the leaves 
were fully exposed to the free air. It was now to be ob- 
served whether the water that exhaled from the leaves 
could be supplied by the hygroscopic moisture Avhich the 
soil should gather from the damp air enveloping it. This 
proved to be the case. The leaves, previously wilted, re- 
covered their proper turgidity, and remained fresh during 
the two months of June and July. 

Sachs, having shown in other experiments that plants 
situated precisely like this bean, save that the roots are not 
in contact with soil, lose water continuously and have no 
power to recover it from damp air (p. 36) thus gives us 
demonstration that the clay soil which condenses vapor in 
its pores and holds it as hygroscopic water, yields it again 
to the plant, and thus becomes the medium through which 



THE FREE WATER OF THE SOIL. 209 

water is continually carried from the atmosphere into 
vegetation. 

In a similar experiment, a tobacco plant was employed 
which stood in a soil of humus. This material was also 
capable of supplying the plant Avith water by virtue of 
its hygroscopic power, but less satisfactorily than the clay. 
As already mentioned, these plants, Avhile remaining fresh, 
exhibited no signs of growth. This may be due to the 
consumption of oxygen by the roots and soil, or possibly 
the roots of plants may require an occasional drenching 
with liquid water. Further investigations in this direc- 
tion are required and j^romise most interesting results. 

What Proportion of the Capillary and Hygroscopic 
Water of the Soil may Plants Absorb, is a question that 
Dr. Sachs has made the only attempts to answer. When 
a j^lant, whose leaves are in a very moist atmosphere, wilts 
or begins to wilt in the night time, when therefore trans- 
piration is reduced to a minimum, it is because the soil no 
longer yields it water. The quantity of water still con- 
tained in a soil at that juncture is that which the plant 
cannot remove from it, — is that which is unavailable to 
vegetation, or at least to the kind of vegetation experi- 
mented with. Sachs made trials on this principle with 
tobacco plants in three different soils. 

The plant began to wilt in a mixture of hlack humus 
(from beech-wood) and sanely when the soil contained 
12.3° |„ of water.* This soil, however, was capable of 
holding 46" 1 3 of capillary water. It results therefore that 
of its highest content of absorbed water 33.7° |, (=46-12.3) 
Avas available to the tobacco plant. 

Another plant began to wilt on a rainy night, Avhile the 
loam it stood in contained 8°| ^ of water. This soil was 
able to absorb 52.1°| ^ of water, so that it might after 



Ascertained by di-ying at 212°. 



210 HOW CROPS FEED. 

saturation, furnish the tobacco plant with 44.1° j^ of its 
weight of water. 

A coarse sand that could hold 20.8° |„ of water Avas 
found to yield all but 1.5° |„ to a tobacco plant. 

From these trials we gather with at least approximate 
accuracy the power of the plant to extract water from 
these several soils, and by difference, the quantity of wa- 
ter in them that was unavailable to the tobacco plant. 

How do the Roots take Hyi^roscopic Water from the 
Soil I — The entire plant, when living, is itself extremely 
hygroscopic. Even the dead plant retains a certain pro- 
portion of water with great obstinacy. Thus wheat, 
maize, starch, straw, and most air-dry vegetable substances, 
contain 12 to 15° 1^ of water; and when these matters are 
exposed to damp air, they can take up much more. Ac- 
cording to Troramer [Bodenkmide^ p. 270), 100 parts of 
the following matters, when diy, absorb from moist air in 

12 24 48 72 







hours. 


"" 


'ine cut barley straw, 


15 


24 34 


45 parts of water. 


" " rye " 


12 


20 27 


29 " " " 


" " white unsized paper, 


8 


12 17 


19 " " '* 



As already explained, a body is hygroscopic because 
there is attraction between its particles and the particles 
of water. The form of attraction exerted thus among 
different kinds of matter is termed adhesive attraction, or 
simply adhesion. 

Adhesion acts only through a small distance, but its in- 
tensity varies greatly within this distance. If we attempt 
to remove hygroscopic water from starch or any similar 
body by drying at 212°, we shall find that the greater 
part of the moisture is easily expelled in a short time, 
but we shall also notice that it requires a relatively much 
longer time to expel the last portions. A general law of 
attraction is that its force diminishes as the distance be- 
tween the attractincr bodies increases. This has been ex- 



THE FREE WATEK OF THE SOIL. 211 

actiy demonstrated in case of the force of gravity and 
electrical attraction, which act through great intervals of 
space. 

We must therefore suppose that when a mass of hygro- 
scopic matter is allowed to coat itself with water by the 
exercise of its adhesive attraction, the layer of aqueous 
particles which is in nearest contact is more strongly held 
to it than the next outer layer, and the adhesion diminish- 
es with the distance, until, at a certain point, still too 
small for us to j^erceive, the attraction is nothing, or is' 
neutralized by other opposing forces, and further adhesion 
ceases. 

Suppose, now, we bring in contact at a single point two 
masses of the same kind of matter, one of which is satu- 
rated with hygroscopic water and the other is perfectly dry. 
It is plain that the outer layers of water-particles adhering 
to the moist body come at once within the range of a 
more powerful attraction exerted by the very surface of 
the dry body. The external particles of water attached 
to the first must then pass to the second, and they must 
also distribute themselves equally over the surface of the 
latter ; and this motion must go on until the attraction 
of the two surfaces is equally satisfied, and the water is 
equally distributed according to the surface, i. e., is uni- 
form over the whole surface. 

If of two difierent bodies jDut in contact (one dry and 
one moist) the surfaces be equal, but the attractive force 
of one for water be twice that of the other, then motion 
must go on until the one has appropriated two-thirds, and 
the other is left with one-third the total amount of water. 

When bodies in contact have thus equalized the water 
at their disposal, they may be said to be in a condition of 
hygroscopic equilibrium. Any cause which disturbs this 
equilibrium at once sets up motion of the hygroscopic 
water, which always j^roceeds from the more dry to the 
less dry body. 



212 HOW CHOPS feed. 

The application of these principles to the question be- 
fore us is apparent. The young, active roots that are in 
contact with the soil are eminently hygroscopic, as is de- 
monstrated by the fact that they supj^ly the plant with 
large quantities of water when the soil is so dry that it 
has no visible moisture. They therefore share with the 
soil the moisture which the latter contains. As water 
evaporates from the surface of the foliage, its place is 
supplied by the adjacent portions, and thus motion is es- 
tablished within the plant which j^ropagates itself to the 
roots and through these to the soil. 

Each particle of water that flies off in vapor from the 
leaf makes room for the entrance of a particle at the root. 
If the soil and air have a surplus of water, the plant will 
contain more ; if the soil and air be dry, it Will contain 
less. Within certain narrow hmits the supply and waste 
may vary without detriment to the plant, but when the 
loss goes on more rapidly than the supply can be kept up, 
or when the absolute content of water in the soil is re- 
duced to a certain point, the plant shortly wilts. Even 
then its content of Avater is many times greater than that 
of the soil. The living tobacco j^lant cannot contain less 
than 80" Iq of water, Avhile the soils in Sachs' experiments 
contained but 12.3° 1^ and 1.5° !„ respectively. When fully 
air-dry, vegetable matter retains 13°|Qto 15° 1^ of water, 
while the soil similarly dry rarely contains more than 

1-21.- 

The plant therefore, especially when living, is much 

more hygroscopic than the soil. 

If roots are so hygroscopic, why, it may be asked, do 
they not directly absorb vapor of water from the air of 
the soil ? It cannot be denied that both the roots and fo- 
liage of plants are capable of this kind of absorption, 
and that it is taking place constantly in case of the roots. 
The experiments before described prove, however, that 
the higher orders of plants absorb very little in this way, 



THE FREE WATER OF THE SOIL. 213 

too little, in fact, to be estimated by the methods hitherto 
employed. Sachs explains this as follows : Assuming that 
the roots have at a given temperature as strong an attrac- 
tion for water in the state of vapor as for liquid water, the 
amount of each taken up in a given time under the same 
circumstances would be in proportion to the weight of 
each contained in a given space. A cubic inch of water 
yields at 212° nearly a cubic foot (accurately, 1,696 times 
its volume, the barometer standing at 29.92 inches) of 
vapor. We may then assume that the absorption of liq- 
uid or hygroscopic water proceeds at least one thousand 
times more rapidly than that of vapor, a difference in 
rate that enables us to comprehend why a plant may gain 
water by its roots from the soil, when it would lose water 
by its roots were they simply stationed in air saturated 
with vaj^or. 

Again, the soil need not be more hygroscopic than roots, 
to supply the latter with water. It is important only that 
it present a sufficient surface. As is well known, a plant 
requires a great volume of earth to nourish it properly, 
and the root-surface is trifling, comj^ared to the surface 
of the particles which compose the soil. 

Boussingault found by actual measurement that, accord- 
ing to the rules of garden culture as practiced near Stras- 
burg, a dwarf bean had at its disposition 57 pounds of 
soil ; a 2:)otato plant, 190 pounds ; a tobacco plant, 470 
pounds ; and a hop plant, 2,900 pounds. These weights 
correspond to about 1, 3, 7, and 50 cubic feet respectively. 

The Quantity of Water in Vegetation is influenced by 

that of the Soil, — De Saussure observed that plants grow- 
ing in a dry lime soil contained less water than those from 
a loam. It is well known that the grass of a wet summer 
is taller and more succulent, and the green crop is heavier 
than that from the same field in a dry summer. It does 
not, however, make much more hay, its greater weight 
consisting to a large degree of water, which is lost in dry- 



214 HOW CROPS PEED. 

ing. Ritthausen gives some data concerning two clover 
crops of the year 1854, from a loamy sand, portions of 
which were manured, one with ashes, others with gypsum. 
The following statement gives the produce of the nearly* 
fresh and of the air-dry crops. 

Weight in pounds per acre. 



Crop I, manured witli ashes, 

" " unmanured, 
Crop II, manured with gypsum, 

" " uumanurcd, 


Fresh. 
14,903- 
12,380 
22,256 

18,815 


Air-dry. 
5,182 
5,418 
4,800 
5,190 


Water lost iu drying. 

9,721 

6,962 
17,456 
13,625 



It is seen that while in both cases the fresh manured 
crop greatly outweighed the unmanured, the excess of 
weight consisted of water. In fact, the unmanured plots 
yielded more hay than the manured. The manured clover 
was darker in color than the other, and the stems were 
large and hollow, i. e., by rapid growth the pith cells were 
broken away from each other and formed only a lining 
to the stalk, while in the unmanured clover the pith re- 
mained undisturbed, the stems being more compact in 
structure. (H. C. G., p. 369.) 

The Quantity of Soil-water most favorable to Crops 

has been studied by Ilienkoif and Hellriegel. The former 
(Ann. der. Chem. ii. Ph. 136, p. 160,) experimented with 
buckwheat plants stationed in pots filled with garden 
earth. The pots were of the same size and had the same 
exposure at the south side of an apartment. The j)lants 
received at each waterinir in 



Pot No. 


1, 


M, 


liter of water 


(( a 


2, 


■1. 


u 


u 


li u 


3, 


■1. 


(( 


a 


a u 


4, 


'1. 


a 


u 


u u 


5, 


'L 


u 


u 



* The clover was collected from the surface of a Saxon square ell, and was 
somewhat wilted before coming into Ritthauscn's hands. The quantities above 
given are calculated to English acres and pounds. 



THE FREE WATER OF THE SOIL. 



215 



The waterings were made simultaneously at the moment 
when all the Avater previously given to No. 1 was ab- 
sorbed by the soil. During the 67 days of the experi- 
ment the plants were watered IT times. The subjoined 
table gives the results : 





Weight of 


Weight of 








fresh Crops in 


dry C'?vps in 


Number of 


Liters of 


Ko. of pot. 


grams. 


grams. 


Seeds. 


water used. 






STRAAV. 


SEEDS. 






1 


27.99 


4.52 


1.08 


Ill 


25.0 


2 


05.05 


8.47 


5.47 


283 


12.5 


3 


24.95 


4.55 


1.73 


93 


6.25 


4 


9.98 


1.41 


0.52 


37 


3.12 


5 


2.30 


0.30 


0.09 


12 


1.56 



The experiment demonstrates that the quantity of 
water supplied to a plant has a decided eifect upon the 
yield. Pot No. 2 was most favorably situated in this re- 
spect. No. 1 had a surplus of water and the other pots 
received too little. The experiment does not teach what 
proportion of water in the soil was most advantageous, 
for neither the weight of the soil nor the size of the pot 
is mentioned. 

Hellriegel {Chem. AcTcersmann, 1868, p. 15) experiment- 
ed with wheat, rye, and oats, in a pure sand mixed with a 
sufficiency of plant-food. The sand when saturated with 
water contained 25° \^ of the liquid. The following table 
gives further particulars of his experiments and the re- 
sults. The weights are grams. 



■WATER IN THE SOIL. 


YIELD OF 


WHEAT. 


YIELD OF RYE. 


YIELD OP OATS. 


In per cent 
of Sou. 


In 2)er cent 

of retentive 

power. 


Straw 
and 
Chaff. 


Grain. 


Straw 
and 
Chaff. 


Grain. 


Straw 
and 
Chaff. 


Grain. 


21/2-5 
5 -10 
10 -15 
15 -20 


10-20 
20-40 
40-60 
60-80 


7.0 
15.1 
21.4 
23.3 


2.8 
8.4 
10.3 
11.4 


8.3 
11.8 
15.1 
16.4 


3.9 
8.1 
10.3 
10.3 


4.2 
11.8 
13.9 
15.8 


1.8 

7.8 

10.9 

11.8 



In each case the proportion of water in the soil was 
preserved within the limits given in the first column of 
the table, throughout the entire period of growth. It is 
seen that in this sandy soil 10-15 per cent of "water ena- 



216 HOW CROPS FEED. 

bled rye to yield a maximum of grain and brought wheat 
and oats very closely to a maximum crop. Ilellriegel no- 
ticed that the plants exhibited no visible symptoms of 
deficiency of water, except through stunted growth, in 
any of these experiments. Wilting never took place ex- 
cept when the supply of water was less than 2' \^ per cent. 

Grouven {Jleher den Zusammenhang zwischen Wit- 
terioig, JBoden und Dimgung in ihrem Einflusse auf die 
Quant itdt und Qualitat der JErndten^ Glogau, 1868) gives 
the results of an extensive series of field trials, in which, 
among other circumstances, the influence of water upon 
the crops was observed. His discussion of the subject is 
too detailed to reproduce in this treatise, but the great 
influence of the supply of water (by rain, etc.,) is most 
strikingly brought out. The experimental fields were 
situated in various parts of Germany and Austria, and 
were cultivated with sugar beets in 1862, under the same 
fertilizing applications, as regards both kind and quantity. 
Of 14 trials in which records of the rain-fall were kept, 
the 8 best crops received from the time of sowing, May 
1st, to that of harvesting, Oct. 15th, an average quantity 
of rain equal to 140 Paris lines in depth. The 6 poorest 
crops received in the same time on the average but 115 
lines. During the most critical period of growth, viz., 
between the 20th of June and the 10th of September, the 
8 best crops enjoyed an average rain-fall of 90.7 lines, 
while the 6 poorest received but 57.7 lines. 

It is a well recognized fact that next to temperature, 
the water supply is the most influential factor in the prod- 
uct of a crop. Poor soils give good crops in seasons of 
plentiful and Avell-distributed rain or when skillfully irri- 
gated, but insufficient moisture in the soil is an evil that 
no supplies of j^lant-^ood can neutralize. 

The Functions of Water in the Nourishment of 
Vegetation, so far as we know them, are of two kinds. 



THE FKEE WATER OF THE SOIL. 217 

In the first place it is an unfailing and sufficient source of 
its elements, — hydrogen and oxygen, — and undoubtedly 
enters directly or indirectly into chemical combination 
with the carbon taken up from carbonic acid, to form sug- 
ar, starch, cellulose, and other carbohydrates. In the 
second place it performs important physical offices ; is the 
vehicle or medium of all tlie circulation of matters in the 
plant ; is directly concerned, it would appear, in imbibing 
gaseous food in the foliage and solid nutriment through 
the roots ; and by the force w4th which it is absorbed, di- 
rectly influences the enlargement of the cells, and, per- 
haps, also the direction of their expansion, — an effect shown 
by the facts just adduced relative to the clover crops ex- 
amined by Ritthausen. 

Indirectly, also, water performs the most important ser- 
vice of continually solving and making accessible to crops 
the solid matters in the vicinity of their roots, as has 
been indicated in the chapter on the Origin of Soils. 

COMbincd Water ©f the Soil. — As already stated, there 
may exist in the soil compounds of which water is a chemi- 
cal component. True clay (kaolinite) and the zeolites, as 
w^ell as the oxides of iron that result from weathering, con- 
tain chemically combined water. Hence a soil which has 
been totally deprived of its hygroscopic water by drying 
at 212°, may, and, unless consisting of pure sand, does, 
yield a further small amount of w^ater by exjjosure to a 
higher heat. This combined water has no direct influence 
on the life of the plant or on the character of the soil, ex- 
cept so far as it is related to the properties of the com- 
pounds of which it is an ingredient. 



THE AIR OF THE SOIL. 

As to the free Oxygen and Nitrogen which exist in the 
interstices or adliere to the particles of the soil, there is 
10 



218 HOW CKOPS FEED. 

little to add here to what has been remarked in previous 
paragraphs. 

Free Oxygen, as De Saussure and Traube have shown, 
is indispensable to growth, and must therefore be access- 
ible to the roots of plants. 

The soil, being eminently porous, condenses oxygen. 
Blumtritt and Reichardt indeed found no considerable 
amount of condensed oxygen in most of the soils and sub- 
stances they examined (p. 167) ; but the experiments of 
Stenhouse (p. 169) and the well-known deodorizing effects 
of the soil upon fecal matters, leave no doubt as to the 
fact. The condensed oxygen must usually spend itself in 
chemical action. Its proportion Avould appear not to be 
large ; but, being replaced as rapidly as it enters into com- 
bination, the total quantity absorbed may be considera- 
ble. Organic matters and lower oxides are thereby ox- 
idized. Carbon is converted into carbonic acid, hydrogen 
into water, j^rotoxide of iron into peroxide. The upper 
portions of the soil are constantly suffering change by the 
action of free oxygen, so long as any oxidable matters 
exist in them. These oxidations act to solve the soil and 
render its elements available to vegetation. (See p. 131.) 

Free Nitrogen in the air of the soil is doubtless indiffer- 
ent to vegetation. The question of its conversion into 
nitric acid or ammonia will be noticed presently. (See p. 
259.) 

Carbonic Acid .—The air of the soil is usually richer in 
carbonic acid, and poorer in oxygen, than the normal at- 
mosphere, while the proportion (by volume) of nitrogen 
is the same or very nearly so. The proportions of car- 
bonic acid by weight in the air included in a variety of 
soils have already been stated. Here follow the total 
quantities of this gas and of air, as well as the composi- 
tion of the latter in 100 parts by volume, as determined by 



THE AIR OF THE SOIL. 



219 



Boussingault and Lewy. 
etc., p. 369.) 



(Memoires de Chimie Agricole, 



Sandy subsoil of forest 

Loamy " " " 

Surface soil " " 

Clayey " of artichoke field 

Soil of asparagus bed not manured for one year 

" " " " newly manured 

Sandy soil, six days after manuring.. . . [of rain 

" " ten '' " " three days 
Vegetable mold-compost 



^ . 


•Pb 








«^ 


-§:§ 




•gs 


^-^ 








Cmnposition of the 




air in tlie soil in 100 


1^ 


parts by volume. 


.;^^^ 


Car- 


Ox- 


Mtro- 


^^ 


=Si 


add. 


ygen. 


gen. 


4416 


14 


0.24 






3530 


28 


0.79 


19. G6 


79.55 


5891 


57 


0^87 


19.61 


79.52 


10310 


71 


0.06 


19.99 


79.35 


11182 


86 


0.74 


19.02 


80.24 


11182 


172 


1.54 


18.80 


79.66 


11783 


257 


2.21 






11783 


1144 


9.74 


10.35 


79.91 


21049 


772 


3.64 


10.45 


79.91 


<» • 


tj 




§1 


s^ 




Is.* 






IS 


e 1^ 




^ 




Composition of air 


$>>s'fe^ 


above the soil in 100 


S-S 


^, s;^ 


parts. 


■N^ 


<i;^.!S-- 








•55 «<; 


Car- 
bon ic 


Ox- 


Nitro- 


c § 




acid. 


ygen. 


gen. 


50820 


12 


0.025 


20.945 


79.030 



The percentage, as well as the absolute quantity of car- 
bonic acid, is seen to stand in close relation with the or- 
sranic matters of the soil. The influence of the recent 
application of manure rich in organic substances is strik- 
ingly shown in case of the asparagus bed and the sandy 
soil. The lowest percentage of carbonic acid is 10 times 
that of the atmosphere a few feet above the surface of the 
earth, as determined at the same time, while the highest 
percentage is 390 times that proportion. 

Even in the sandy subsoil the quantity of free carbonic 
acid is as great as in an equal bulk of the atmosphere ; 
and in the cultivated soils it is present in from 6 to 95 



220 HOW CROPS FEED. 

times greater amount. In other words, in the cultivated 
soils taken to the depth of 14 inches, there was found as 
much carbonic acid gas as existed in the same horizontal 
area of the atmosphere through a height of 7 to 110 feet. 

The accumulation of such a percentage of carbonic acid 
gas in the interstices of the soil demonstrates the rapid 
formation of this substance, which must as rapidly diifuse 
off into the air. The roots, and, what is of more signifi- 
cance, the leaves of crops, are thus fiir more copiously fed 
with this substance than were they simply bathed by the 
free atmosphere so long as the latter is unagitated. 

When the wind blows, the carbonic acid of the soil is 
of less account in feeding vegetation compared with that 
of the atmosphere. When the air moves at the rate of 
two feet per second, the current is just plainly perceptible. 
A mass of foliage 2 feet high and 200 feet * long, situated 
in such a current, would be swept by a volume of atmos- 
phere, amounting in one minute to 48,000 cubic feet, and 
containing 12 cubic feet of carbonic acid. In one hour it 
would amount to 2,280,000 cubic feet of air, equal to 720 
cubic feet of carbonic acid, and in one day to 69,120,000 
cubic feet of air, containing no less than 17,280 cubic feet 
of carbonic acid. 

In a brisk wind, ten times the above quantities of air 
and carbonic acid would pass by or through the foliage. 
It is plain, then, that the atmosphere, which is rarely at 
rest, can supply carbonic acid abundantly to foliage with- 
out the concourse of the soil. At the same time it should 
not be forgotten that the carbonic acid of the atmosphere 
is largely derived from the soil. 

Carbonic Acid in the Water of the Soil.— Notwith- 
standing the presence of so much carbonic acid in the air 
of the soil, it appears that the capillary soil-water, or so 



A square field containing onQ acre is 208 feet and a few inches on each side. 



THE AIR OF THE SOIL. 221 

much of it as may be expressed by pressure, is not nearly 
saturated with this gas. 

De Saussure {Recherches Chimiques sur la Vegetation, 
p. 168) filled large vessels with soils rich in organic mat- 
ters, poured on as much water as the earth could imbibe, 
allowing the excess to drain off and the vessels to stand 
five days. Then the soils were subjected to powerful 
pressure, and the water thus extracted was examined for 
carbonic acid. It contained but 2° \^ of its volume of the 
gas. 

Since at a medium temperature (60° F.) water is capa- 
ble of dissolving 100" |„ (its own bulk) of carbonic acid, it 
would appear on first thought inexplicable that the soil- 
water should hold but 2 per cent. Henry and Dalton long 
ago demonstrated that the relative proportion in which 
the ingredients of a gaseous mixture are absorbed by wa- 
ter depends not only on the relative solubility of each gas 
by itself, but also on the proportions in which they exist 
in the mixture. The large quantities of oxygen, and 
especially of nitrogen, associated with carbonic acid in the 
pores of the soil, thus act to prevent the last-named gas 
being taken up in greater amount ; for, while carbonic 
acid is about fifty times more soluble than the atmos- 
pheric mixture of oxygen and nitrogen, the latter is pres- 
ent in fifty times (more or less) the quantity of the former. 

Absorption of Carbonic Acid by the Soil, — ^According to 
Van den Broek, {Ann. der Chemie \l. Ph., 115, p. 87) certain 
wells in the vicinity of -Utrecht, Holland, which are exca- 
vated only a few feet deep in the soil of gardens, contain 
water which is destitute of carbonic acid (gives no precipi- 
tate with lime-water), while those which penetrate into the 
underlying sand contain large quantities of carbonate of 
lime in solution in carbonic acid. 

Van den Broek made the following experiments with 
garden-soil newly manured, and containing free carbonic 
acid in its interstices, which could be displaced by a cur- 



222 HOW CROPS PEED. 

rent of air. Through a mass of this earth 20 inches deep 
and 3 inches in diameter, pure distilled water (free 
from carbonic acid) was allowed to filter. It ran through 
without tahing \ip any of the gas. Again, water contain- 
ing its own volume of carbonic acid was filtered through 
a similar body of the same earth. This water gave up all 
its carbonic acid while in contact icith the soil. After a 
certain amount had run off", however, the subsequent por- 
tions contained it. In other words, the soils experiment- 
ed with were able to absorb carbonic acid from its aqueous 
solution, even when their interstices contained the gas in 
the free state. These extraordinary phenomena deserve 
further study. 

§ 3. 

NON-NITROGENOUS ORGANIC MATTERS OF THE SOIL.— 

CARBOHYDRATES. VEGETABLE ACIDS. VOLATILE 

ORGANIC ACIDS. HUMUS. 

Carbohydrates, or Bodies of the Cellulose Group. — 

The steps by which organic matters become incorporated 
with the soil have been recounted on p. 135. When i3lants 
perish, their proximate principles become mixed with the 
soil. These organic matters shortly begin to decay or to 
pass into humus. In most circumstances, however, the 
soil must contain, temporarily or ^periodically, unalter- 
ed carbohydrates. Cellulose, especially, may be often 
found in an unaltered state in the form of fragments of 
straw, etc. 

De Saussure {Recherches, ^. 174) found that water dis- 
solved from a rich garden soil that had been highly ma- 
nured for a long time, several thousandths of organic 
matter, giving an extract, which, when concentrated, had 
an almost syrupy consistence and a' sweet taste, was 
neither acid nor alkaline in reaction, and comported itself 
not unlike an impure mixture of glucose and dextrin. 



ORGANIC MATTERS OF THE SOIL. 223 

Verdeil and Risler have made similar observations on ten 
soils from the farm of the Institut Agronomique^ at Ver- 
sailles. They found that the water-extract of these soils 
contained, on the average, 50° j^ of organic matter, which, 
when strongly heated, gave an odor like burning paper or 
sugar. These observers make* no mention of crenates or 
apocrenates, and it, perhaps, remains somewhat doubtful, 
therefore, whether their researches really demonstrate the 
presence in the soil of a neutral body identical with, or 
allied to, dextrin or sugar. 

Cellulose, starch, and dextrin, pass by fermentation into 
sugar (glucose) ; this may be resolved into lactic acid (tlie 
acid of sour milk and sour-krout), butyric acid (one of the 
acids of rancid butter), and acetic acid (the acid of vine- 
gar). It must often happen that the bodies of the cellu- 
lose group ferment in the soil, the same as in the souring 
of milk or of dough, though they suffer for the most part 
conversion into humus, as will be shortly noticed. 

Vegetable Acids, viz., oxalic, malic, tartaric, and citric 
acids, become inirredients of the soil when vesretable mat- 
ters are buried in it. When the leaves of beets, tobacco, 
and other large-leaved plants fall upon the soil, oxalic and 
malic acids may pass into it in considerable quantity. 
Falling fruits may give it citric, malic, and tartaric acids. 
These acids, however, speedily suffer chemical change 
when in contact with decaying albuminoids. Buchner has 
shown {Ann. Ch. u. Ph.^ 78, 207) that the solutions of 
salts of the above-named vegetable acids are raj^idly con- 
verted into carbonates when mixed with vegetable fer- 
ments. In this process tartaric and citric acids are first 
partially converted into acetic acid, and this subsequently 
passes into carbonic acid. 

Volatile Organic Acids. — Formic, propionic, acetic, and 
butyric acids, or rather their salts, have been detected by 
Jongbloed and others in garden earth. They are common 



224 now CKOrs feed. 

products of fermentation, n process that goes on in the 
jnices of plants that have become a part of the soil or of 
a compost. 

These acids can scarcely exist in the soil, except tempo- 
rarily, as results of fermentation or decay, and then in but 
very minute quantity. They consist of carbon, hydrogen, 
and oxygen. Their salts are all freely soluble in water. 
Then- relations to agricultnral plants have not been studied. 

Humus (in ])art). — The general nature and origin of 
humus has been already considered. It is the debris of 
vegetation (or of animal matters) in certain stages of de- 
composition. Humus is considerably complex in its 
chemical character, and our knowledge of it is confessedly 
incomplete. In the paragraphs that immediately follow, 
we shall give from the best sources an account of its non- 
nitrogenous ingredients, so far they are understood, reserv- 
ing to a later chapter an account of its nitrogenized con- 
stituents. 

The Non-iiitro^eiiows Components of Humus. — The 

appearance and composition of humus is different, accord- 
ing to the circumstances of its formation. It has already 
been mentioned that humus is brown or black in color. 
It appears that the first stage of decomposition yields the 
brown humus. It is seen in the dead leaves hanging to a 
tree in autumn, in the upper layers of fallen leaves, in the 
outer bark of trees, in the smut of wheat, and in the uj> 
per, dryer portions of peat. 

When brown humus remains wet and with imperfect 
access of air, it decomposes further, and in time is convert- 
ed into black humus. Black humus is invariably found 
in the soil beyond a little dej^th especially if it be com- 
pact, in the deeper layers of peat, in the interior of com- 
post heaps, in the lower portions of the leaf-mould of 
forests, and in the mud or muck of swamps and ponds. 

Ulmic Acid and Ulmin. — The brown humus contains 



ORGANIC MATTERS OF THE SOIL. 225 

(besides, perliaj^s, unaltered vegetable matters) two char- 
acteristic ingredients, which have been designated ulmic 
acid and idmin, (so nnmed from having been found in a 
brown mass that exuded from an elm tree, ulmus being 
the Latin for elm). These two bodies demand particular 
notice. 

When brown peat is boiled with water, it gives a yel- 
lowish or pale-brown liquid, being but little soluble in 
pure water. If, however, it be boiled with dilute solution 
of carbonate of soda (sal-soda), a dark-brown liquid is 
obtained, which owes its color to ulmate of soda. The 
alkali dissolves the insoluble ulmic acid by combining 
with it to form a soluble compound. By repeatedly heat- 
ing the same portion of j^eat with new quantities of sal- 
soda solution, and pouring off the liquids each time, there 
arrives a moment when the peat no longer yields any color 
to the solution. The brown j^eat is thus separated mto 
one portion soluble, and another insoluble, in carbonate of 
soda. TJhnic acid has passed into the solution, and ulmin^ 
remains undissolved (mixed, it may be, with unaltered 
vegetable matters, recognizable by their form and struc- 
ture, and with sand and mineral substances). 

By adding hydrochloric acid to the brown solution as 
long as it foams or effervesces, the ulmic acid separates in 
brown, bulky flocks, and is insoluble in dilute hydrochloric 
acid, but is a little soluble in pure water. When moist, it 
has an acid reaction, and dissolves readily in alkalies or 
alkali-carbonates. On drying, the ulmic acid shrinks 
greatly and remains as a brown, coherent mass. 

The ulmin^ which remains after treatment of brown 
peat with carbonate of soda is an indifferent, neutral (i. e., 
not acid) body, which has the same composition as the 



* The above statement is made on the authority of Mulder. The -writer has, 
however, found, in several cases, that continued treatment with carbonate of 
soda alone completely dissolves the humus, leaving a residue of cellulose which 
yields nothing to caustic alkali. He is, therefore, inclined to disbelieve in the 
cxisteuce of ulmin and humin as distinct from ulmic and humic acida. 



226 HOW CROPS FEED. 

ulmic acid. By boiling it with caustic soda or potash-lye, 
it is converted without change of composition into ulmic 
acid. 

On gently heating sugar with dilute hydrochloric acid, 
a brown substance is produced, which appears to be iden- 
tical with the ulmic acid obtained from peat. 

Huniic Acid and Humin. — By treating black humus 
with carbonate of soda as above described, it is separated' 
into kumic acid and humin^^ which closely resemble ulmic 
acid and ulmin in all their properties — possess, however, a 
black color, and, as it appears, a somewhat different com- 
position. 

Humic acid and humin may be obtained also by the 
action of hot and strong hydrochloric acid, of sulphuric 
acid, and of alkalies, upon sugar and the other members 
of the cellulose group. 

Composition of llmin, Ulmic Acid, Humin, and Humic 
Acid, — The results of the analyses of these bodies, as ob- 
tained by different experimenters and from different 
sources, are not in all cases accordant. Either several dis- 
tinct substances have been confounded under each of the 
above names, or the true ulmin and humin, and ulmic and 
humic acids, are liable to occur mixed with other matters, 
from which they cannot be or have not been perfectly 
separated. 

Mulder {Chemie der AckerJcrume, 1, p. 322), who has 
chiefly investigated these substances, believes there is a 
group of bodies having in general the characters of ulmin 
and ulmic acid, whose composition differs only by the ele- 
ments of water,f and is exhibited by the general formula 

C„ H„ 0„ + nH,0, ^ 
in which nH^O signifies one, two, three, or more of water. 



* See note on page 225. 

t In a way analogous to what is known of the sugars. (H. C. G., p. 80.) 



ORGANIC MATTERS OF THE SOIL. 227 

Ulmic acid from sugar has the following composition iu 
100 parts : 

Carbon, 67.1 

Hydrogen, 4.2 

Oxygen, 28.7 



100.0 
which corresponds to C^^ H^^ O^^ H^O. 

Mulder considers that in the same mamier there exist 
various kinds of humic acids and humin, differing from 
each other by the elements of water, all of which may 
be represented by the general formula C^„ H^^ O^^ nH„0. 
Humic acid and humin from sugar, corresponding to 
C^, H^, O,^ + ^^fi, have, according to Mulder, the fol- 
lowing composition per cent : 

Carbon, 64 

Hydrogen, 4 

Oxygen, 32 



100 



Apocrenic and Crenic Acids. — In the acid liquid from 
which ulmic or humic acid has been separated, exist two 
other acids which were first discovered by Berzelius in 
the Porla spring in Sweden, and which bear the names 
apocrenic acid and crenic acid respectively. By adding 
Boda to the acid liquid until the hydrochloric acid is neu- 
tralized, then acetic acid in slight excess, and lastly solu- 
tion of acetate of copper (crystallized verdigris) as long 
as a dirty-gray precipitate is formed, the apocrenic acid is 
procured in combination with copper and ammonia. From 
this salt the acid itself may be separated* as a brown, 
gummy mass, which is easily soluble in water. Accord- 
ing to Mulder it has the formula C^^ H^^ Oj, + H„0, or, 
in 100 parts. 



By precipitating the copper with sulphuretted hydrogen. 



2:28 HOW CHOPS feed. 

Carbon, 5G.47 
Hydrogen, 2.75 
Oxygen, 40.78 



100.00 
Crenate of copper is lastly precipitated as a grass-green 
substance by adding acetate of copper to the liquid from 
which the apocrenate of copper was separated, and then 
neutralizino^ the free acid with ammonia. From this com- 
pound crenic acid may be prepared as a white, solid body 
of sour taste, to which Mulder ascribes the formula C^^ 
■^24 ^16 "^ ^H^O, and in 100 parts the following compo- 
sition • 

Carbon, 45.70 

Hydrogen, 4.80 

Oxygen, 49.50 



100.00 
Mutual Conversion of Apocrenic and Crenic Acids. 

— When, on the one hand, apocrenic acid is placed in 
contact with zinc and dilute sulphuric acid, the hydrogen 
evolved from the latter converts the brown apocrenic acid 
(by uniting Avith a portion of its oxygen) mto colorless 
crenic acid. On the other liand, the solution of crenic 
acid exposed to the air shortly becomes brown by absor])- 
tion of oxygen and formation of apocrenic acid. These 
changes may be repeated many times with the same por- 
tion of these substances. 

Mulder remarks ( Chemie der AcJcerJcrume, p. 350) : 
" In every fertile soil these acids always occur together in 
not inconsiderable quantities. When the earth is turned 
over by the j^low, two essentially different processes fol- 
low each other : oxidation, where the air has free access ; 
reduction, Avhere its access is more or less limited by the 
adhesion of the particles and especially by moisture. In 
the loose, dry earth apocrenic acid is formed ; in the firm, 



ORGANIC MATTERS OP THE SOIL. 229 

moist soil, and in every soil after rain, crenic acid is pro- 
duced, so that the action or effects of these substances are 
alternately manifested." 

The Humus Bodies Artificially Produced. — When 

sugar, cellulose, starch, or gum, is boiled with strong liy- 
drochloric acid or a strong sohition of potash, brown or 
black bodies result which have the greatest similarity with 
the ulmin and humin, the ulmic and humic acids of peat 
and of soils. 

By heating humus with nitric acid (a vigorous oxidizing 
agent), crenic and apocrenic acids are formed. The pro- 
duction of these bodies by such artificial means gives in- 
teresting confirmation of the reality of their existence, 
and demonstrates the correctness of the views which have 
been advanced as to their origin. 

While the precise composition of all these substances 
may well be a matter of doubt, and from the difficulties 
of obtaining them in the pure state is likely to remain so, 
their existence in the soil and their importance in agricul- 
tural science are beyond question, as we shall shortly have 
opportunity to understand. 

Tlie Condition of these Humus Bodies in the Soil 

requires some comment. The organic substances thus 
noticed as existing in the soil are for the most part acids, 
but they do not exist to much extent in the free state, ex- 
cept in bogs and morasses. A soil that is fit for agricul- 
tural purposes contains little or no free acid, except car- 
bonic acid, and oftentimes gives an alkaline reaction with 
test-papers. 

Regarding ulmic and humic acids, which, as we have 
stated, are extracted by solution of carbonate of soda 
from humus, it appears that they do not exhibit acid char- 
acters before treatment with the alkali. They appear to 
be altered by the alkali and converted through its Influ- 
ence into acids. Only those portions of these bodies 



230 HOW CROPS FEED. 

which are acted upon by the carbonates of potash, soda, 
and lime, that become ingredients of the soil by the 
solution of rocks, or by carbonate of ammonia brought 
down from the atmosphere or produced by decay of ni- 
trogenous matters, acquire solubility, and are, in fact, 
acids; and these portions are acids in combination (salts), 
and not in the free state. 

The Salts of the Humus Acids that may exist in the 
soil, viz., the ulmates, humates, apocrenates, and erenates 
of potash, soda, ammonia, lime, magnesia, iron, manga- 
nese, and alumina, require notice. 

The ulmates and humates agree closely in their charac- 
ters so far as is known. 

The ulmates and humates of the alkalies (potash, soda, 
and ammonia) are freely soluble in water. They are formed 
when the alkalies or their carbonates come in contact 1st, 
with the ulmic and humic acids themselves ; 2d, with the 
ulmates and humates of lime, magnesia, iron, and manga- 
nese ; and 3d, by the action of the alkalies and their car- 
bonates on humin and ulmin. Their solutions are yellow 
or brown. 

The ulmates and humates of lime, magnesia, iron, man- 
ganese, and alumina, are insoluble^ or but very slightly 
soluble ill water. 

From ordinary soils where these earths and oxides pre- 
dominate, water removes but traces of humates and 
ulmates. 

From peat, garden earth, and leaf-mould, which contain 
excess of- the humic and ulmic acids, and carbonate of 
ammonia resulting from the decay of nitrogenous matters, 
water extracts a perceptible amount of these acids render- 
ed soluble by the alkali. 

Th^re appear to exist double salts of humic acid and of 
ulmic acid, i. e,, salts containing the acid combined with two 
or more bases. By adding solutions of compounds (e. g., 
sulphates) of lime, magnesia, iron, manganese, and alumina 



ORGANIC MATTERS OF THE SOIL. 231 

to solutions of humates or ulmates of the alkalies, precipi- 
tates are formed in which the acid is combined both with 
an alkali and an earth or oxide. These double salts are 
insoluble or nearly so in water. 

Solutions of alkalies and alkali carbonates decompose 
them into soluble alkali humates or ulmates, and the 
earths or oxides are at least partially held in solution by 
the resulting compounds. _^ 

Mulder describes the following experiments, wliich justifj^ the above 
conclusions. "Garden-soil was extracted with dilute solution of car- 
bonate of soda, the soil being in excess. The solution was filtered and 
precipitated by addition of water, and the precipitate was Avashed and dis- 
solved in a little ammonia. Thus Avas obtained a dark -brown solution 
of neutral humate of ammonia. The solution was rendered perfectly 
colorless by addition of caustic lime — basic humate of lime is therefore 
perfectly insoluble in water. 

"Chloride of calcium rendered the solution very nearly colorless — 
neutral humate of lime is almost entirely insoluble. 

" Calcined magnesia decolorized the solution perfectly. Chloride of 
magnesium made the solution very nearly colorless. 

"The sulphates of protoxide and peroxide of iron, and sulphate of 
manganese, decolorized the solution perfectly. 

"These decolorized liquids Averc made broAvn again by agitating them 
and the precipitated humates with carbonate of ammonia." 

Apocrenates and €renates. — According to Mulder, the 
crenates and apocrenates of the soil nearly always contain 
ammonia — are, in fact, double salts of this alkali with lime, 
iron, etc. 

The apocrenates of the alkalies are freely soluble; 
those of the oxides of iron and manganese are moderately 
soluble; those of lime, magnesia, and alumina, are in- 
soluble. 

The crenates of the alkalies, of lime, magnesia, and 
protoxide of iron, are soluble ; those of protoxide of iron 
and manganese are less soluble; crenate of alumina is 
insoluble. 

All the salts of these acids that are insoluble of them- 
selves are decomposed by, and soluble in, excess of the 
alkali-salts. 



Ii61i HOW CHOPS FEED. 

Do the Organic Matters of the Soil Directly Nourish 
Vegetation ? — This is a question which, so far as humus is 
concerned, has been discussed with great earnestness by 
the most prominent writers on Agricultural Science. 

De Saussure, Berzelius, and Mulder, have argued in the 
affirmative ; while Liebig and his numerous adherents to- 
tally deny to humus the possession of any nutritive value. 
It is probable that humus may be directly absorbed by, 
and feed, plants. It is certain, also, that it does not con- 
tribute largely to the sustenance of agricultural crops. 

To ascertain the real extent to which humus is taken up 
by plants, or even to demonstrate that it is taken up by 
them, is, j^erhaps, impossible from the data now in our 
possession. We shall consider the probabilities. 

There have not been wanting attempts to ascertain ex- 
perimentally whether humus is capable of feeding vegeta- 
tion. Hartig, De Saussure, Wiegmann and Polstorf, and 
Soubeiran, liave observed the growth of plants whose 
roots were immersed in solutions of humus. The experi- 
ments of Hartig led this observer to conclude that humate 
of 2)otasli and water-extract of peat do not enter the roots 
of i^lants. ISTot having had access to the original account 
of this investigation, the writer cannot, perhajDS, judge 
properly of its merits. It appears, however, that the 
roots of the plants operated with were not kept constantly 
moist, and their extremities were decomposed by too great 
concentration of the liquid in which they were immersed. 
Under such conditions accurate results were out of the 
question. 

De Saussure {A?in. Ch. ii. PA., 42, 275) made two ex- 
periments, one with a l>ean, the other with Polygonum 
'Pe/rsicaria^ in which these plants were made to vegetate 
with their roots immersed in a solution of humate of pot- 
ash (prepared by boiling humus with bicarbonate of pot- 
ash). In the first case the bean plant, originally weighing 
11 grams, gained during 14 days G grms., while the 



ORGANIC MATTERS OF THE SOIL. 233 

weight of the humus decreased 9 milligrams. The 
Polygonum during 10 days gained 3,5 gims., and the 
solution lost 43 milligrams of humus. These experi- 
ments Liebig considers undecisive, because an alkali- 
humate loses weight by oxidation (to carbonic acid and 
water) when exposed in solution to the air. Mulder, how- 
ever, denies that any appreciable loss could occur in such 
a solution during the time of experiment, and considers 
tlie trials conclusive. 

In a third experiment, De Saussure j^laced the roots of 
Polygonum Persicaria in the water-extract of turf con- 
taining no humic acid but crenic and apocrenic acids, 
where they remained nine days in a very flourishing state, 
putting forth new roots of a healthy white color. An 
equal quantity of the same extract was placed in a simi- 
lar vessel for purposes of comparison. It was found that 
the solution in which the plants were stationed became 
paler in color and remained perfectly clear, while the other 
solution retained its original dark tint and became turbid. 
The former left after evaporation 33 mgrms.,the latter 39 
mgrms. of solid residue. The difference of 6 mgrms., De 
Saussure believes to have been absorbed by the plant. 

Wiegmann and Polstorf ( Ueber die unorganischen Pe- 
standtheile der PJlanzen) experimented in a similar man- 
ner Avith Mentha undnlata^ a kind of mint, and Polygonum 
Persicaria^ using two plants of 8 inches height, whose 
roots were well developed and j)erfectly healthy. The 
l^lants grew for 30 days in a wine-yellow water-extract 
of leaf compost (containing 148 mgrms. of solid sub- 
stance — organic matter, carbonate of lime, etc., — in 100 
grams of extract), the roots being shielded from light, 
and during the same time an equal quantity of the same 
solution stood near by in a vessel of the same dimensions. 
The plants grew well, increasing 6|- inches in length, and 
put forth long roots of a healthy white color. On the 
18th of July the plants were removed from the solution, 



234 HOW CROPS FEED. 

and 100 grams of the solution left on evaporation 132 
mgrras. of residue. The same amount of humus extract, 
that had been kept in a contiguous vessel containing no 
plant, left a residue of 136 mgrms. The disappearance of 
humus from the solution is thus mostly accounted for by- 
its oxidation. 

De Saussure considers that his experiments demonstrate 
that humic acid and (in his third exj).) the matters ex- 
tracted from peat by water (crenic and apocrenic acids) 
are absorbed by plants. Wiegmann and Polstorf attrib- 
ute any apparent absorption in their. trials to the una- 
voidable errors of experiment. The quantities that may 
have been absorbed were indeed small, but in our judg- 
ment not smaller than ought to be estimated with certainty. 

Other experiments by Soubeiran, Malaguti, and Mulder, 
are on record, mostly agreeing in this, viz., that agricul- 
tural plants (beans, oats, cresses, peas, barley) grow well 
when their roots are immersed in, or watered by, solutions 
of humates, ulmates, crenates, and apocrenates of ammo- 
nia and potash. These experiments are, however, all un- 
adaj^ted to demonstrate that humus is absorbed by plants, 
and the trials of De Saussure and of Wiegmann, and Pol- 
storf, are the only ones that have been made under condi- 
tions at all satisfactory to a just criticism. These do not, 
perhaps, conclusively demonstrate the nutritive function 
of humus. It is to be observed, however, that what evi- 
dence they do furnish is in its favor. They prove effec- 
iTually that humus is not injurious to plants, though Liebig 
and Wolif have strenuously insisted that it is poisonous. 

Let us now turn to the probabilities bearing on the 
question. 

In the first place there are j)lants — those living in bogs 
and flourishing in dung-heap liquor — which throughout 
the whole period of their growth must tolerate^ if not ab- 
sorb, somewhat strong solutions of humus. 

Again, the cultivated soil invariably yields some humus 



ORGANIC MATTERS OF THE SOIL. 235 

(we use this word as a general collective term) to rain- 
water, and the richer the soil, as made so by manures and 
judged of by its productiveness, the larger the quantity, 
uj) to certain limits, of humus it contains. If, as we have 
seen, plants always contain silica, though this element be 
not essential to their development (H. C. G., p. 186), is it 
probable that they are able to reject humus so constantly 
presented to them under such a variety of forms ? 

Liebig opposes the view that humus contributes directly 
to the nourishment of plants because it and its compounds 
are insoluble ; in the same book, however, (Die Chemie 
in ihrer Anwendung auf Agricultur tmd Physiologic, 
7th Ed., 1862) he teaches the doctrine that all the food 
of the agricultural plant exists in the soil in an insoluble 
form. This old objection, still maintained, tallies poorly 
with his new doctrine. The old objection, furthermore, is 
baseless, for the hu mates are as soluble as phosphates, 
which are gathered by every plant and from all soils. 

It has been the habit of Liebig and his adherents to 
teach that the plant is nourished exclusively by the last 
products of the destruction of organic matter, viz., by car- 
bonic acid, ammonia, nitric acid, and water, together with 
the ingredients of ashes. AVhile no one denies or doubts 
that these substances chiefly nourish agricultural plants, 
no one can deny that other bodies may and do take part 
in the process. It is well established that various organic 
substances of animal origin, viz., urea, uric acid, and gly- 
cocoll, are absorbed by, and nourish, agricultural plants ; 
while it is universally known that the principal food of 
multitudes of the lower orders of plants, the fungi, includ- 
ing yeast, mould, rust, brand, mushrooms, are fed entirely, 
so far as regards their carbon, on organic matters. Thus, 
yeast lives upon sugar, the vinegar plant on acetic acid, 
the Peronospora infestcms on the juices of the potato, 
etc. There are many parasitic plants of a higher order 
common in our forests whose roots are fastened upon and 



236 HOW CKOPS FEED. 

absorb the juices of the roots of trees ; such are the beech 
drops {Epiphegus)^ pine drops (Pterospora), Indian pipe 
(Mo)iotropa); the last-named also grows upon decayed 
vegetable matter. 

The dodder ( Ct/scuta) is parasitic upon living plants, 
especially upon flax, whose juices it appropriates often to 
the destruction of the crop. 

It is indeed true that there is a wide distinction between 
most of these parasites and agricultural plants. The 
former are mostly destitute of chlorophyll, and aj^pear to 
be totally incapable of assimilating carbon from carbonic 
acid.* The latter acquire certainly the most of their food 
from carbonic acid, but in their root-organs they contain 
no chlorophyll; there they cannot assimilate carbon from 
carbonic acid. They do assimilate nitrogen from the or- 
ganic principles of urine ; what is to hinder their obtain- 
ing carbon from the soluble portions of humus, from the 
organic acids, or even from unaltered carbohydrates? 

De Saussure, in his investigation just quoted from, says 
further : " After having thus demonstrated f the absorp- 
tion of humus by the roots, it remains to speak of its as- 
similation by the plant. One of the indications of this 
assimilation is derived from the absence of the peculiar 
color of humus in the interior of the plant, which has ab- 
sorbed a strongly colored solution of humate of potash, as 
compared to the diiferent deportment of coloring matters 



* Dr. Luck (Ann. Chem. u. Pliarm., 78, 85) has indeed shown that the mistle- 
toe ( Viscum album) decomposes carbonic acid in the sunlight, but this plant has 
greenish-yellow leaves containing chlorophyll. 

t "We take occasion here to say explicitly that the only valid criticism of De 
Sanssure's experiment on the Polygonum supplied \vith humate of potash, is 
Liebig's, to the etFect that the solution lost humic acid to the amount of 43 milli- 
grams not as a result of absorption by the plant, but by direct oxidation. 
Mulder and Soubeiran both agree that such a solution could not lose perceptibly 
in this way. Tliat De Saussure was satisfied that such a loss could not occur, 
would appear from the fact that he did not attempt to estimate it, as he did in 
the subsequent experiment with water-extract of peat. If, now, Liebig be wrong 
in his objection (and he has furnished no proof that his statement is true), then 
De Saussure has demonstrated that humic acid is absorbed by plants. 



orga:n^ic matiers of the soil. 23T 

(such as ink) which cannot nourish the plant. The latter 
(ink, etc.) leave evidences of their entrance into the plant, 
while the former are changed and partly assimilated. 

"A bean 15 inches high, whose roots were placed in a 
decoction of Brazil-wood (to which a little alum had been 
added and which was filtered), was able to absorb no more 
than the fifth part of its weight of this solution without 
wilting and dying. In this process four-fifths of its stem 
was colored red. 

'■'' Pol yg Oman Persicaria (on occasion an aquatic or bog 
plant) grew very well in the same sohition and absorbed 
its coloring matter, but the color never reached the stem. 
The red principle of Brazil-wood being partially assimilat- 
ed by the Polygonum,^ underwent a chemical change; 
while in the bean, which it was unable to nourish, it suf- 
fered no change. The Polygonum, itself became colored, 
and withered when its roots were immersed in diluted 
ink." 

Biot (Comptes Mendus, 1837, 1, 12) observed that the 
red juice of Phytolacca decandra (poke-weed), when 
poured upon the soil in which a white hyacinth was blos- 
soming, was absorbed by the plant, and in one to two 
hours dyed the flowers of its own color. After two or 
three days, however, the red color disappeared, the flow- 
ers becoming white again. 

From the facts just detailed, we conclude that some 
kinds of organic matters may be absorbed and chemically 
changed (certain of them assimilated) by agricultural 
plants. 

We must therefore hold it to be extremely probable 
that various forms of humus, viz., soluble humates, ulmates, 
crenates, and apocrenates, together with the other soluble 
organic matters of the soil, are taken up by plants, and 
decomposed or transformed, nay, we may say, assimilated 
by them. 



238 HOW CKOPS FEED. 

A few experiments might easily be devised which would 
completely settle this point beyond all controversy. 

Organic Matters as Indirect Sources of Carbon to 
PlantSt — The decay of organic matters in the soil supplies 
to vegetation considerably more carbonic acid in a given 
time than would be otherwise at the command of crops. 
The quantities of carbonic acid found in various soils have 
already been given (p. 219). The beneficial effects of such 
a source of carbonic acid in the soil are sufficiently obvious 
(p. 128). 

Ori^anic Matters not Essential to tlie Growth of 
Crops. — Although, on the farm, crops are rarely raised 
without the concurrence of humus or at least without its 
presence in the soil, it is by no means indispensable to 
their life or full development. Carbonic acid gas is of it- 
self able to supply the rankest vegetation with carbon, as 
has been demonstrated by numerous experiments, in which 
all other compounds of this element have been excluded 
(p. 48). 

§4. 
THE AMMONIA OF THE SOIL. 

In the chapter on the Atmosphere as the food of plants 
we have been led to conclude that the element nitrogen, 
so indispensable to. vegetation as an ingredient of albumin, 
etc., is supplied to plants exclusively by its compounds^ 
and mainly by ammonia and nitric acid, or by substances 
which yield these bodies readily on oxidation or decay. 

We have seen further that both ammonia and nitric acid 
exist in very minute quantities in the atmosphere, are dis- 
solved in the atmospheric waters, and by them brought 
into the soil. 

It is pretty fairly demonstrated, too, that these bodies, 
as occurring in the atmosphere, become of appreciable use 



THE AMMOXIA OF THE SOIL. 239 

to agricultural vegetation only after tlieir incorporation 
with the soil. 

Rain and dew are means of collecting them from the 
atmosphere, and, as we shall shortly see, the soil is a 
storehouse for them and the medium of their entrance into 
vegetation. 

This is therefore the proper place to consider in detail 
the origin and formation of ammonia and nitric acid, so 
far as these points have not been noticed when discussing 
their relations to the atmosphere. 

Ammonia is formed in the Soil either in the decay of 
organic bodies containing nitrogen, as the albuminoids, 
etc., or by the redaction of nitrates (p. 74). The former 
process is of universal occurrence since both vegetable 
and animal remains are constantly present in the soil ; the 
latter transformation goes on only under certain condi- 
tions, which will be considered in the next section (p. 
269). 

The statement that ammonia is generated from the free 
nitrogen of the air and the nascent hydrogen of decom- 
posing carbohydrates, as cellulose, starch, etc., or that set 
free from water in the oxidation of certain metals, as iron 
and zinc, has been completely disproved by Will. {Ami. 
d. Gh. u. Ph., 45, pp. 100-112.) 

The ammonia encountered in such experiments may have been, 1st, 
that pre-existinj;- in the pores of tlie substances, or dissolved in the wa- 
ter operated witli. Faraday {Researches in Chemistry arid Physics, p. 143) 
has sliowu by a series of exact experiments that numerous, we may say 
all, porous bodies exposed to the air have a minute amount of ammonia 
adhering to them ; 2d, that which is generated in the process of testing 
or experimenting (as when iron is heated with potash), and formed by 
the action of an alkali on some compound of nitrogen occurring in the 
materials of the experiment ; or, 3d, that which results from the reduc- 
tion of a nitrite formed from free nitrogen by the action of ozone (pp. 
77-83). 

The Ammonia of the Soil. — a. Gaseous Ammo?iia as 
Carhonate. — Boussingault and Lewy, in their examination 
of the air contained in the interstices of the soil, p. 219, 



240 HOW CROPS FEED. 

tested it for ammonia. In but two instances did they find 
sufficient to weigh. In all cases, however, they were able 
to detect it, though it was present in very minute quanti- 
ty. The two exj^eriments in which they were able to 
weigh the ammonia were made in a light, sandy soil from 
which potatoes had been lately harvested. On the 2d of 
September the field was manured with stable dung ; on 
the 4th the first experiment was made, the air being taken, 
it must be inferred from the account given, at a depth of 
14 inches. In a million parts of air by weight were found 
32 parts of ammonia. Five days subsequently, after rainy 
weather, the air collected at the same place contained but 
13 parts in a million. ' J" 

h. Aonmonia physically condensed in the Soil. — Many 
porous bodies condense a large quantity of ammonia gas. 
Charcoal, which has an extreme porosity, serves to illus- 
trate this fact. De Saussure found that box-wood char- 
coal, freshly ignited, absorbed 98 times its volume of 
ammonia gas. Similar results have been obtained by Sten- 
house, Angus Smith, and others (p. 166). The soil cannot, 
however, ordinarily contain more than a minute quantity 
of physically absorbed ammonia. The reasons are, first, a 
l^orous body saturated with ammonia loses the greater share 
of this substance when other gases come in contact with 
it. It is only possible to condense in charcoal 98 times its 
volume of ammonia, by cooling the hot charcoal in mer- 
cury which does not penetrate it, or in a vacuum, and then 
bringing it directly into the pure ammonia gas. The 
charcoal thus saturated with ammonia loses the latter rap- 
idly on exposure to the air, and Stenhouse has found by 
actual trial that charcoal exposed to ammonia and after- 
wards to air retains but minute traces of the former. 
Secondly, the soil when adapted for vegetable growth is 
moist or wet. The water of the soil which covers the 
particles of earth, rather than the particles themselves, 
must contain any absorbed ammonia. Thirdly, there are 



THE AMMOXIxV OF THE SOIL. 241 

in fertile soils substances wliicli combine chemically with 
ammonia. 

That the soil does contain a certain quantity of ammo- 
nia adhering to the surface of its particles, or, more prob- 
ably, dissolved in the hygroscopic water, is demonstrated 
by the experiments of Boussingault and Lewy just alluded 
to, in all of which ammonia was detected in the air in- 
cluded in the cavities of the soil. In case ammonia were 
physically condensed or absorbed, a j^ortion of it would 
be carried off in a current of air in the conditions of 
Boussingault and Lewy's experiments, — nay, all of it 
would be removed by such treatment sufficiently prolonged. 

Brustlein (Boussingault's Agronomie^ etc.^ 1, ^. 152) 
records that 100 parts of moist earth placed in a vessel of 
about 2^ quarts capacity containing 0.9 parts of (free) 
ammonia, absorbed during 3 hours a little more than 0.4 
parts of the latter. In another trial 100 parts of the same 
earth dried, placed under the same circumstances, absorb- 
ed 0.28 parts of ammonia and 2.6 parts of water. 

Brustlein found that soil placed in a confined atmos- 
phere containing very limited quantities of ammonia can- 
not condense the latter completely. In an experiment 
similar to those just described, 100 parts of earth (tena- 
cious calcareous clay) and 0.019 parts of ammonia were 
left together 5 days. At the conclusion of this period 
0.016 parts of the latter had been taken up by the earth. 
The remainder was found to be dissolved in the water 
that had evaporated from the soil, and that formed a dew 
on the interior of the glass vessel. 

Brustlein proved further that while air may be almost 
entirely deprived of its ammonia by traversing a long 
column of soil, so the soil that has absorbed ammonia 
readily gives up a large share of it to a stream of pure air. 
He caused air, charged with ammonia gas by being made 
to bubble through water of ammonia, to traverse a tube 1 
ft. long filled with small fragments of moist soil. The 
11 



242 HOW CROPS FEED. 

ammonia was completely absorbed in the first part of the 
experiment. After about 7 cubic feet of air had streamed 
through the soil, ammonia began to escape unabsorbed. 
The earth thus saturated contained 0.192° |g of ammonia. 
A current of pure air was now passed through the soil as 
long as ammonia was removed by it in notable quantity, 
about 38 cubic feet being required. By this means more 
than one-half the ammonia was displaced and carried off, 
the earth retaining but 0.084" |,,. 

Brustlein ascertained further that ammonia which has 
been absorbed by a soil from aqueous solution escapes 
easily when the earth is exposed to the air, especially 
when it is repeatedly moistened and allowed to dry. 

100 parts of the same kind of soil as was employed in 
the experiments already described were agitated with 187 
parts of water containing 0.889 parts of ammonia. The 
earth absorbed 0.157 parts of ammonia. It was now 
drained from the liquid and allowed to dry at a low tem- 
perature, which operation required eight days. It was 
then moistened and allowed to dry again, and this was re- 
peated four times. The progressive loss of ammonia is 
shown by the following figures. 

100 parts of soil absorbed , 0.157 parts of ammonia. 

" " " " contained after the first drying 0.083 " 

" " " " " " " second " 0.066. " 

" " " " " " " third " 0.054 " 

" " " " " " " fourth " 0.041 " 

" " " " " " " fifth " 0.039 " 

In this instance the loss of ammonia amounted to three- 
fourths the quantity at first absorbed. 

The extent to which absorbed ammonia escapes from 
the soil is greatly increased by the evaporation of water. 
Brustlein found that a soil containing 0.067" !„ of ammo- 
nia suffered only a trifling loss by keeping 43 days in a 
dry place, whereas the same earth lost half its ammonia 
in a shorter time by being thrice moistened and dried. 

According to Knop ( Vs. JSt.y III, p. 222), the single 



THE AMMONIA OF THE SOIL. 243 

proximate ingredient of soils that under ordinary cir- 
cumstances exerts a considerable surface attraction for 
ammonia gas is day. Knop examined the deportment of 
ammonia in this respect towards sand, soluble silica, pure 
alumina, carbonate of lime, carbonate of magnesia, hy- 
drated sesquioxide of iron, sulphate of lime, and humus. 

To recapitulate, the soil contains carbonate of ammonia 
physically absorbed in its pores, i. e., adhering to the sur- 
faces of its particles, — as Knop believes, to the particles 
of clay. The quantity of ammonia is variable and con- 
stantly varying, being increased by rain and devt^, or ma- 
nuring, and diminished by evaporation of water. The 
actual quantity of physically absorbed ammonia is, in 
general, very small, and an accurate estimation of it is, 
perhaps, impracticable, save in a few exceptional cases. 

c. Chemically combined Ammonia. — The reader will 
have noticed that in the experiments of Brustlein just 
quoted, a greater quantity of ammonia was absorbed by 
the soil than afterwards escaped, either when the soil was 
subjected to a current of air or allowed to dry after moist- 
ening with water. This ammonia, it is therefore to be be- 
lieved, was in great part retained in the soil in chemical 
combination in the form of compounds that not only do 
not permit it readily to escape as gas, but also are not 
easily washed out by water. The bodies that may unite 
with ammonia to comparatively insoluble compounds are, 
1st, the organic acids of the humus group* — the humus 
acids, as we may designate them collectively. The salts 
of these acids have been already noticed. Their com- 



* Mulder asserts that the affinity of ulmic, humic, and apocrenic acids for 
ammonia is so strong that they can only be freed from it by evaporation of their 
solutions to dryness with caustic potash. Boiling with carbonate of potash or 
carbonate of soda will not suffice to decompose their ammonia-salts. We hold 
it more likely that the ammonia which requires an alkali for its expulsion is 
generated by the decomposition of the organic acid itself, or, if that be desti- 
tute of nitrogen, of some nitrogenous substance admixed. According to Bous- 
singault, ammonia is completely removed from humus by boiling with water and 
caustic magnesia. 



244 HOW CROPS FEED. 

pounds with ammonia are freely soluble in water ; hence 
strong solution of ammonia dissolves them from the soil. 
But when ammonia salts of these acids are put in contact 
with lime, magnesia, oxide of iron, oxide of manganese, 
and alumina, the latter being in preponderating quantity, 
there are formed double compounds which are insoluble 
or slightly soluble. Since the humic, ulmic, crenic, and 
apocrenic acids always exist in soils which contain organic 
remains, there can be no question that these double salts are 
a chemical cause of the retention of ammonia in the soil. 

2d. Certain phosphates and silicates hereafter to be no- 
ticed have the power of forming difficultly soluble com- 
pounds with ammonia. 

Reserving for a subsequent chapter a further discussion 
of the causes of the chemical retention of ammonia in the 
soil, we may now appropriately recount the observations 
that have been made regarding the condition of the am- 
monia of the soil as regards its volatility, solubility, etc. 

Volatility of the Ammonia of the Soil. — We have 
seen that ammonia may escape from the soil as gaseous 
carbonate. The fact is not only true of this substance as 
physically absorbed, but also under certain conditions of 
that chemically combined. When we mingle together 
equal bulks of sulphate of lime (gypsum) and carbonate 
of ammonia, both in the state of fine powder, the mixture 
begins and continues to smell strongly of ammonia, owing 
to the volatility of the carbonate. If now the mixture be 
drenched with water, the odor of ammonia at once ceases 
to be perceptible, and if, after some time, the mixture be 
thrown on a filter and washed with water, we shall find 
that what remains undissolved contains a large proportion 
of carbonate of lime, as may be shown by its dissolving 
in an acid with effervescence ; while the liquid that has 
passed the filter contains sulphate of ammonia, as may be 
learned by the appropriate chemical tests or by evaporat- 
ing to dryness, when it will remain as a colorless, odorless, 



THE AMMONIA OP THE SOIL. 245 

ciystalline solid. Double decomposition has taken place 
between the two salts under the influence of water. If, 
again, the carbonate of lime on the filter be reunited to 
the liquid filtrate and the whole be evaporated, it will be 
found that when the water has so far passed ofi* that a 
moist, pasty mass remains, the odor of ammonia becomes 
evident again — carbonate of ammonia, in fact, escaping by- 
volatilization, while sulj^hate of lime is reproduced. It is 
a general law in chemistry that when a number of acids 
and bases are together, those which under the circum- 
stances can produce by their union a volatile body will 
unite, and those which under the circumstances can form a 
solid body will unite. When carbonic and sulphuric acids, 
lime and ammonia, are in mixture, it is the circumstances 
which determine in what mode these bodies combine. In 
presence of much water carbonate of lime is formed be- 
cause of its insolubility, water not being able to destroy 
its solidity, and sulphate of ammonia necessarily results 
by the union of the other two substances. When the wa- 
ter is removed by evaporation, all the possible compounds 
between carbonic and sulphuric acids, lime and am- 
monia, become solid ; the compound of ammonia and car- 
bonic acid being then volatile, this fact determines its 
formation, and, as it escapes, the lime and sulphuric acid 
can but remain in combination. 

To apply these principles : When carbonate of ammo- 
nia is brought into the soil by rain, or otherwise, it tends 
in presence of much water to enter into insoluble combi- 
nations so far as is possible. When the soil becomes dry, 
these compounds begin to undergo decomposition, provid- 
ed carbonates of lime, magnesia, potash, and soda, are 
present to trans]30se with them ; these bases taking the 
place of the ammonia, while the carbonic acid they Were 
united with, forms with the latter a volatile compound. 
In this way, then, all soils, for it is probable that no soil 
exists which is destitute of carbonates, may give off at the 



246 HOW CROPS FEED. 

surface in dry weather a portion of the ammonia which 
before was chemically retained within it. 

Solubility of the Ammonia of the Soil.— The distinc- 
tions between physically adhering and chemically combin- 
ed ammonia are difficult, if not impossible, to draw with 
accuracy. In what follows, therefore, we shall not attempt 
to consider them separately. 

When ammonia, carbonate of ammonia, or any of the 
following ammoniacal salts, viz., chloride, sulphate, ni- 
trate, and phosphate, are dissolved in water, and the solu- 
tions are filtered through or agitated with a soil, we find 
that a portion of ammonia is invariably removed from so- 
lution and absorbed by the soil. An instance of this ab- 
sorbent action has been already given in recounting 
Brustlein's experiments, and further examples will be here- 
after adduced when we come to speak of the silicates of 
the soil. The points to which we now should direct at- 
tention are these, viz., 1st, the soil cannot absorb ammo- 
nia completely from its solutions ; and, 2d, the ammonia 
which it does absorb may be to a great degree dissolved 
out again by water. In other words, the compounds of 
ammonia that are formed in the soil, though comparatively 
insoluble, are not absolutely so. 

Henneberg and Stohmann found that a light, calcareous, 
sandy garden soil, when placed in twice its weight of pure 
water for 24 hours, yielded to the latter 5o\ o of its weight 
of ammonia (=0.0002" |J. 

100 parts of the same soil left for 24 hours in 200 parts 
of a solution of chloride of ammonium (containing 2.182 
of sal-ammoniac =0.693 part of ammonia), absorbed 0.112 
part of ammonia. Half of the liquid was poured off 
and its place suj^plied with j^ure water, and the whole 
left for 24 hours, when half of this liquid was taken, and 
the process of dilution was thus repeated to the fifth time. 
In the portions of water each time removed, ammonia was 
estimated, and the result was that the water added dis- 



THE AMMONIA OF THE SOIL. 247 

solved out nearly one-half the ammonia which the earth 

at first absorbed. 

The 1st dilution removed from the soil 0,010 

" 2d " " " " " 0.009 

" 3d " " " " " 0.014 

" 4tli " " " " " 0.011 

" 5tli " " " " " 0.009 

Total 0.053 

Deducting 0.053 from the quantity first absorbed, viz.,' 
0.112, there remains 0.059 part retained by the soil after 
five dilutions. Knop, in 11 decantations, in which the 
soil was treated with 8 times its weight of water, removed 
93° |g of the ammonia which the soil had previously ab- 
sorbed. We cannot doubt that by repeating the washing 
sufficiently long, all the ammonia would be dissolved, 
though a very large volume of water would certainly be 
needful. 

Causes which ordinarily prevent the Accumulation of 
Ammonia in the Soil. — The ammonia of the soil is con- 
stantly in motion or suffering change, and does not ac- 
cumulate to any great extent. In summer, the soil daily 
absorbs ammonia from the air, receives it by rains and 
dews, or acquires it by the decay of vegetable and animal 
matters. 

Daily, too, ammonia wastes from the soil — by volatili- 
zation — accompanying the vapor of water which almost 
unceasingly escapes into the atmosphere. 

When the soil is moist and the temperature not too low, 
its ammonia is also the subject of remarkable chemical 
transformations. Two distinct chemical changes are be- 
lieved to affect it ; one is its oxidation to nitric acid. This 
process we shall consider in detail in the next section. As 
a result of it, we never find ammonia in the water of or- 
dinary wells or deep drains, but instead always encounter 
nitric acid united to lime, and, perhaps, to magnesia and 
alkalies. The other chemical change appears to be the 
alteration of the compounds of ammonia with the humus 



248 HOW CROPS FEED. 

acids, whereby bodies result which are no longer soluble 
in water, and which, as such, are probably innutritions to 
plants. These substances are quite slowly decomposed 
when put in contact, especially when heated with alkalies 
or caustic lime in the j^resence of water. In this decom- 
position ammonia is reproduced. These indifferent nitrog- 
enous matters appear to be analogous to a class of sub- 
stances known to chemists as amides, of which asparagin, 
a crystallizable body obtained from asparagus, young peas, 
etc., and urea and uric acid, the characteristic ingredients 
of urine, are examples. Further account of these matters 
will be given subsequently, p. 276. 

Quantity of Ammonia in Soils. — Formerly the amount 
of ammonia in soils was greatly overestimated, as the re- 
sult of imperfect methods of analysis. In 1846, Krocker, 
at Liebig's instigation, estimated the nitrogen of 22 soils, 
and Liebig published some ingenious speculations in which 
all this nitrogen was incorrectly assumed to be in the form 
of ammonia. Later, various experimenters have attempt- 
ed to estimate the ammonia of soils. In 1855, the writer 
examined several soils in Liebig's laboratory. The soils 
were boiled for some hours with water and caustic lime, 
or caustic potash. The ammonia that was set free, distill- 
ed off, and its amount was determined by alkalimetry. 
It was found that however long the distillation was kept 
up, ammonia continued to come over in minute quantity, 
and it was probable that this substance was not simply 
expelled from the soil, but was slowly formed by the ac- 
tion of lime on organic matters, it being well known to 
chemists that many nitrogenous bodies are thus decom- 
posed. The results were as follows : 

Ammonia. 
White sandy loam distilled with caustic lime gave in two Esp's. ■! ^'Pj^P P^t 



Yellow clay 



0.0186 

u cc u u (0.0047 

I 0.0051 

potash " " one " 0.0075 



Black garden soil " " " lime " " two 



0.0831 
0.0953 



THE AMMONIxV OF THE SOIL. 249 

The fact that caustic potash, a more energetic decom- 
posing agent than lime, disengaged more ammonia than 
the latter from the yellow clay, strengthens the view that 
ammonia is produced and not merely driven off under the 
conditions of these experiments, and that accordingly the 
figures are too high. Other chemists employing the same 
method have obtained similar results. 

Boussingault {Agronomie, T. Ill, p. 206) was the first 
to substitute magnesia for potash and lime in the estima-4 
tion of ammonia, having first demonstrated that this sub- 
stance, so feebly alkaline, does not perceptibly decompose 
gelatine, albumin, or asparagine, all of which bodies, espe- 
cially the latter, give ammonia when boiled with milk of 
lime or solutions of potash. The results of Boussingault 
here follow. 

Localities. Quantity of Ammonia per cent. 

Liebfranenberg, Alsatia 0.0023 

Bischwillcr, " 0.0020 

Merckwiller, " 0.0011 

Bechelbronn, " 0.0009 

Mittelbausbcrgen, " 0.0007 

He Napoleon, Mulhouse, 0.0006 

Argentan, Orne, 0.0060 

Quesnoy-sur-Deule, Nord, 0.0012 

Rio Madeira, America, 0.0090 

Eio Trombetto, " 0.0030 

EioNegro, " 0.0038 

Santarem, " 0.0083 

IleduSalut, " 0.0080 

Martinique, " 0.0085 

EioCupari, (leaf mold,) " 0.0525 

Peat, Paris, 0.0180 

The above results on French soils correspond with those 
obtained more recently on soils of Saxony by Knop and 
Wolff, who have devised an ingenious method of estimat- 
ing ammonia, which is founded on altogether a different 
principle. Knop and Wolff measure the nitrogen gas 
which is set free by the action of chloride of soda (Ja- 
velle water *) in a specially constructed apparatus, the 

* More properly hypocMorite of soda, which is used in mixture with bromine 
and caustic soda, 
11* 



250 HOW CROPS FEED. 

Azotometer. ( Chemisches Centralblatt^ 1860, pp. 243 a;nd 
534.) 

By this method, which gives accurate results when ap- 
plied to known quantities of ammonia-salts, Knop and 
Wolff obtained the following results : 

Ammonia in dry soil. 

Very light sandy soil from birch forest .0.00077° |o 

Rich lime soil from beech forest 0.00087 

Sandy loam, forest soil 0.00012 

Forest soil 0.00080 

Meadow soil, red sandy loam 0.00037 

Average 0.00056 

The rich alluvial soils from tropical America are ten or 
more times richer in ready-formed ammonia than those of 
Saxony. These figures show then that the substance in 
question is very variable as a constituent of the soil, and 
that in the ordinary or poorer classes of unmanured soils 
its percentage is scarcely greater than in the atmospheric 
waters. 

The Quantity of Ammonia fluctuates. — Boussingault 
has further demonstrated by analysis what we have insist- 
ed upon already in this chapter, viz., that the quantity of 
ammonia is liable to fluctuations. He estimated ammonia 
in garden soil on the 4th of March, 1860, and then, moist- 
ening two samples of the same soil with pure water, ex- 
amined them at the termination of one and two months 
respectively. He found, 

March 4th, 0.009° |„ of ammonia. 

April " 0.014" " 

May " 0.019 " " " 

The simple standing of the moistened soil for two 
months sufficed in this case to double the content of am- 
monia. 

The quantitative fluctuations of this constituent of the 
soil has been studied further both by Boussingault and 
by Knop and Wolff". The latter in seeking to answer the 



THE NITRIC ACID OF THE SOIL. 251 

question — " How great is the ammonia-content of good 
manured soil lying fallow?" — made repeated determina- 
tions of ammonia (17 in all) in the same soil (well-ma- 
nured, sandy, calcareous loam exposed to all rains and 
dews but not washed) during five months. The moist 
soil varied in its proportion of ammonia with the greatest 
irregularity between the extremes of 0.0008 and 0.0003" l^,. 
Similar observations were made the same summer on the 
loamy soil of a field, at first bare of vegetation, then cov- 
ered with a vigorous potato crop. In this case the fluctu- 
ations ranged from 0.0009 to 0.0003" 1^ as irregularly as in 
the other instance. 

Knop and Wolff examined the soil last mentioned at 
various depths. At 3 ft. the proportion of ammonia was 
scarcely less than at the surface. At 6 ft. this loam, and 
at a somewhat greater depth an underlying bed of sand, 
contained no trace of ammonia. This observation ac- 
cords with the established fact that deep well and drain- 
waters are destitute of ammonia. 

Boussingault has discovered {Agronomie^ 3, 195) that 
the addition of caustic lime to the soil largely increases its 
content of ammonia — an efiect due to the decomposing ac- 
tion of lime on the amide-like substances already noticed. 

§5. 

NITRIC ACID (NITRATES, NITROUS ACID, AND NITRITES) OF 
THE SOIL. 

Nitric acid is formed in the atmosphere by the action 
of ozone, and is brought down to the soil occasionally in 
the free state, but almost invariably in combination with 
ammonia, by rain and dew, as has been already described 
(p. 86). It is also produced in the soil itself by processes 
whose nature — considerably obscure and little understood 
' — will be discussed presently. 



252 HOW CKOPS FEED. 

In the soil, nitric acid is always combined with an 
alkali or alkali-earth, and never exists in the free state in 
appreciable quantity. We speak of nitric acid instead of 
nitrates, because the former is the active ingredient com- 
mon to all the latter. Before considering its formation 
and nutritive relations to vegetation, we shall describe 
those of its compounds which may exist in the soil, viz., 
the 7iitrates of potash^ soda^ llme^ magnesia^ and iron. 

Nitrate of Potash (K NOJ is the substance com- 
mercially known as niter or saltpeter. When pure (refin- 
ed saltpeter), it occurs in colorless prismatic crystals. It 
is freely soluble in water, and has a j^eculiar sharp, cooling 
taste. Crude saltj^eter contains common salt and other 
impurities. Nitrate of j^otasli is largely procured for in- 
dustrial uses from certain districts of India (Bengal) and 
from various caves in tropical and temperate climates, by 
simply leaching the earth with Avater and evaporating the 
solution thus obtained. It is also made in artificial niter- 
beds or plantations in many European countries. It is 
likewise prepared artificially from nitrate of soda and 
caustic potash, or chloride of potassium. The chief use 
of the commercial salt is in the manufacture of gunpowder 
and fireworks. 

Sulphur, charcoal, (which are ingredients of gunpow- 
der), and other combustible matters, when heated in con- 
tact with a nitrate, burn with great intensity at the ex- 
l^ense of the oxygen which the nitrate contains in large 
proportion and readily parts with. 

Nitrate of Soda (Na NO3) occurs in immense quantities 
in the southern extremity of Peru, province of Tarapaca, 
as an incrustation or a compact stratum several feet thick, 
on the pampa of Tamarngel, an arid plain situated in a 
region where rain never falls. The salt is dissolved in hot 
water, the solution poured ofi" from sand and evaporated to 
the crystallizing point. The crude salt has in general a 



THE NITRIC ACID OF THE SOIL. 253 

yellow or reddish color. When pure, it is white or color- 
less. From the shape of the crystals it has been called 
cubic* niter; it is also known as Chili saltpeter, having 
been formerly exported from Chilian ports, and is some- 
times termed soda-saltpeter. In 1854, about 40,000 tons 
were shipped from the port of Iquique. 

Kitrate of soda is hygroscopic, and m damp air be- 
comes quite moist, or even deliquesces, and hence is not 
suited for making gunpowder. It is easily procured arti- 
ficially by dissolving carbonate of soda in nitric acid. 
This salt is largely employed as a fertilizer, and for pre- 
paring nitrate of potash and nitric acid. 

Nitrate of Lime (Ca2N'03) may be obtained as a white 
mass or as six-sided crystals by dissolving lime in nitric 
acid and evaporating the solution. It absorbs water from 
the air and runs to a liquid. Its taste is bitter and sharp. 
Nitrate of lime exists in well-waters and accompanies 
nitrate of potash in artificial niter-beds. 

Nitrate of Magnesia (Mg2N03) closely resembles ni- 
trate of lime in external characters and occurrence. It 
may be prepared by dissolving magnesia in nitric acid and 
evaporating the solution. 

Nitrates of Iron. — Various compounds of nitric acid 
and iron, both soluble and insoluble, are known. In the 
soil it is probable that only insoluble basic nitrates of 
sesquioxide can occur. Knop observed ( K St., V, 151) 
that certain soils when left in contact with solution of ni- 
trate of potash for some time, failed to yield the latter en- 
tirely to water again. The soils that manifested this 
anomalous deportment were rich in humus, and at the 
same time contained much sesquioxide of iron that could 
be dissolved out by acids. It is possible that nitric acid 
entered into insoluble combinations here, though this 
hypothesis as yet awaits proof 

♦ The crystals are, in fact, rhomboidal. 



254 HOW CROrs feed. 

Nitrates of alumina are known to the chemist, but have 
not been proved to exist in soils. Nitrate of ammonia 
has already been noticed, p. 71. 

Nitric Acid not usually fixed by the Soil. — In its deport- 
ment towards the soil, nitric acid (either free or in its salts) 
differs in most cases from ammonia in one important par- 
ticular. The nitrates are usually not fixed by the soil, but 
remain freely soluble in water, so that washing readily and 
completely removes them. The nitrates of ammonia and 
potash are decomposed in the soil, the alkali being retain- 
ed, while the nitric acid may be removed by washing with 
water, mostly in the form of nitrate of lime. Nitrate of 
soda is partially decomposed in the same manner. Free 
nitric acid unites with lime, or at least is found in the 
washings of the soil in combination with that base. 

As just remarked, Knop has observed that certain soils 
containing much organic matters and sesquioxide of iron, 
appeared to retain or decompose a small portion of nitric 
acid (put in contact with them in the form of nitrate of 
potash). Knop leaves it uncertain whether this result is 
simply the fault of the method of estimation, caused by 
the formation of basic nitrate of iron, which is insoluble in 
water, or, as is perhaps more probable, due to the de- 
composing (reducing) action of organic matters. 

Nitrification is the formation of nitrates. When vege- 
table and animal matters containing nitrogen decay in the 
soil, nitrates of these bases presently appear. In Bengal, 
during the dry season, when for several months rain sel- 
dom or -never falls, an incrustation of saline matters, 
chiefly nitrate of potash, accumulates on the surface of 
those soils, which are most fertile, and which, though culti- 
vated in the wet season only, yield two and sometimes 
three crops of grain, etc., yearly. The formation of ni- 
trates, which probably takes place during the entire year, 
appears to go on most rapidly in the hottest weather. 



THE NITKIC ACID OF THE SOIL. 255 

The nitrates accumulate near the surface when no rain 
falls to dissolve and wash them down — when evaporation 
causes a current of capillary water to ascend continually 
in the soil, carrying with it dissolved matters which must 
remain at the surface as the water escapes into the atmos- 
phere. In regions where rain frequently falls, nitrates are 
largely formed in rich soils, but do not accumulate to any 
extent, unless in caves or positions artificially sheltered 
from the rain. 

Boussingault's examination of garden earth from Lieb- 
frauenberg {Agronomie, etc., T. II, p. 10) conveys an idea 
of the progress which nitrification may make in a soil un- 
der cultivation, and highly charged with nitrogenous ma- 
nures. About 2.3 lbs. of sifted and well-mixed soil were 
placed in a heap on a slab of stone under a glazed roof. 
From time to time, as was needful, the earth was moist- 
ened with water exempt from ammonia. The proportion 
of nitric acid was determined in a sample of it on the day 
the experiment began, and the analysis was repeated four 
times at various intervals. The subjoined statement gives 
the per cent of nitrates expressed as nitrate of potash in 
the dry soil, and also the quantity of this salt contained 
in an acre taken to the depth of one foot.* 





Per cent. 


Zbs. 


. per acre. 


857— 5th August, 


0.01 




34 


" -17th 


0.06 




222 


" — 2d September, 


0.18 




634 


" -17th " 


0.23 




760 


*' — 2d October, 


0.21 




728 



The formation of nitrates proceeded rapidly during the 
heat of summer, but ceased by the middle of September. 
Whether this cessation was due to the lower temperature 
or to the complete nitrification of all the matter existing 
in the soil capable of this change, or to decomposition 
of nitric acid by the reducing action of organic matters, 

* The figures given above are abbreviated from the originals, or reduced to 
English denominations with a trifling loss of exactness. 



256 HOW CROPS FEED. 

further researches must decide. The quantities that ac- 
cumulated in this experiment are seen to be very consider- 
able, when we remember that experience has shown that 
200 lbs. per acre of the nitrates of potash or soda is a 
large dressing upon grain or grass. Had the earth been 
exposed to occasional rain, its analysis would have indi- 
cated a much less percentage of nitrates, because the salt 
would have been washed down far into, and, perhaps, 
out of, the soil but no less, probably even somewhat 
more, would have been actually formed. In August, 1856, 
Boussingault examined earth from the same garden after 14 
days of hot, dry weather. He found the nitrates equal to 
911 lbs. of nitrate of potash per acre taken to the depth of 
one foot. From the 9th to the 29th of August it rained 
daily at Liebfrauenberg, more than two inches of water 
falling during this time. When the rain ceased, the soil 
contained but 38 lbs. per acre. In September, rain fell 15 
times, and to the amount of four inches. On the 10th of 
October, after a fortnight of hot, windy weather, the gar- 
den had become so dry as to need watering. On being 
then analyzed, the soil was found to contain nitrates equiv- 
alent to no less than 1,290 lbs. of nitrate of potash per 
acre to the depth of one foot. This soil, be it remembered, 
was porous and sandy, and had been very heavily manur- 
ed with well-rotted compost for several centuries. 

Boussingault has examined more tlian sixty soils of ev- 
ery variety, and in every case but one found an apprecia- 
ble quantity of nitrates. Knop has also estimated nitric 
acid in several soils ( Versuchs JSt., Y, 143). Nitrates are 
almost invariably found in all well and river waters, and 
in quantities larger than exist in rain. We may hence as- 
sume that nitrification is a process universal to all soils, 
and that nitrates are normal, though, for the reasons stat- 
ed, very variable ingredients of cultivated earth. 

The Sources of the Nitric Acid which is formed within 
the Soil. — Nitric acid is produced — a, from ammoniay 



THE ]^ITRIC ACID OF THE SOIL. 257 

either that absorbed by the soil from the atmosphere, or 
that originating in the soil itself by the decay of nitrog- 
enous organic matters. Knop made an experiment with 
a sandy loam, as follows : The earth was exposed in a box 
to the vapor of ammonia for three days, was then mixed 
thoroughly, spread out thinly, moistened with pure water, 
and kept sheltered from rain until it became dry again. 
At the beginning of the experiment, 1,000,000 parts of 
the earth contained 52 parts of nitric acid. During its 
exjDOSure to the air, while moist, the content of nitric acid 
in this earth increased to 591 parts in 1,000,000, or more 
than eleven times ; and, as Knop asserts, this increase took 
j^lace at the expense of the ammonia which the earth had 
absorbed. The conversion of ammonia into nitric acid is 
an oxidation expressed by the statement 

2 NH3 + 40 = NH^ NO3 + II.O. * 
The oxygen may be either ozone, as already explained, 
or it may be furnished by a substance which exists in all 
soils and often to a considerable extent, viz., sesquioxide 
of iron. This compound (Fe^ O3) readily yields a portion 
of its oxygen to bodies which are inclined to oxidize, be- 
ing itself reduced thereby to protoxide (FeO) thus : — 
Fe^ O3 - 2 FeO 4- O. The protoxide in contact with the 
air quickly absorbs common oxygen, passing into sesqui- 
oxide again, and in this way iron operates as a carrier of 
atmospheric oxygen to bodies which cannot directly com- 
bine with the latter. The oxidizing action of sesquioxide 
of iron is proved to take place in many instances ; for ex- 
ample, a rope tied around a rusty iron bolt becomes " rot- 
ten," cotton and linen fibrics are destroyed by iron-stains, 
the head of an iron nail corrodes aw^ay the w^ood sur- 
rounding it, when exposed to the weather, and after suf- 



* The above equation represents bnt one-half of the ammonia as converted 
into nitric acid. In the soil the carbonates of lime, etc., would separate the 
nitric acid from the remaining ammonia and leave the latter in a condition to 
be oxidized. 



258 HOW CROPS FEED.. 

ficient time this oxidation extends so far as to leave the 
board loose upon the nail, as may often be seen on old, 
unpainted wooden buildings. Direct experiments by Knop 
( Versuchs St., Ill, 228) strongly indicate that ammonia is 
oxidized by the agency of iron in the soil. 

b. The organie matters of the soil, either of vegetable 
or animal origin, which contain nitrogen, suffer oxidation 
by directly combining with ordinary oxygen. 

As we shall presently see, nitrates cannot be formed in 
the rapid or putrefactive stages of decay, but only later, 
when the process proceeds so slowly that oxygen is in large 
excess. "When the organic matters are so largely dilut- 
ed or divided by the earthy parts of the soil that oxygen 
greatly preponderates, it is probable that the nitrogen of 
the organic bodies is directly oxidized to nitric acid. 
Otherwise ammonia is first formed, which is converted in- 
to nitrates at a subsequent slower stage of decay. 

Nitrogenous organic matters may perhaps likewise yield 
nitric acid when oxidized by the intervention of hydrated 
sesquioxide of iron, or other reducible mineral compounds. 
Thenard mentions ( Comptes Mendus, XLIX, 289) that a 
nitrogenous substance obtained by him from rotten dung 
and called fumic acid^ when mixed with carbonate of 
lime, sesquioxide of iron and water, and kept hot for 15 
days in a closed vessel, was oxidized with formation of 
carbonic acid and noticeable quantities of nitric acid, the 
sesquioxide being at the same time reduced to protoxide. 

The various sulphates that occur in soils, especially sul- 
phate of lime (gypsum, plaster), and sulphate of iron 
(copperas), may not unlikely act in the same manner to 
convey oxygen to oxidable substances. These sulphates, 
in exclusion of air, become reduced by organic matters to 
sulphides. This often happens in deep fissures in the 
earth, and causes many natural waters to come to the sur- 



* According to Mulder, impure humate of ammonia. 



THE NITEIC ACID OF THE SOIL. 259 

face charged with sulphides (sulphur-springs). Water 
containing sulphates in solution often acquires an odor of 
sulphuretted hydrogen by being kept bottled, the cork or 
other organic matters deoxidizing the sulphates. The 
earth just below the paving-stones in Paris contains con- 
siderable quantities of sulphides of iron and calcium, the 
gypsum in the soil being reduced by organic matters. 
(Chevreul.) These sulphides, when exposed to air, speed- 
ily oxidize to sulphates, to suffer reduction again in con- 
tact with the appropriate substances, and under certain 
conditions, operate continuously, to gather and impart 
oxygen. One of the causes of the often remarkable and 
inexplicable effects of plaster of Paris when used as a fer- 
tilizer may, perhaps, be traced to this power of oxidation, 
resulting in the formation of nitrates. This point requires 
and is well worthy of special investigation. 

c. Lastly, the free nitrogen of the atmosphere appears 
to be in some way involved in the act of nitrification — is 
itself to a certain extent oxidized in the soil, as has been 
maintained by Saussure, Gaultier de Claubry, and others 
( QmelirCs JSand-hooh of Chemistry^ II, 388). 

The truth of this view is sustained by some of Bous- 
singault's researches on the garden soil of Liebfrauenberg 
{Agronomie, etc., T., 1, 318). On the 29th of July, 1858, 
he spread out thinly 120 grammes of this soil in a shallow 
glass dish, and for three months moistened it daily with 
water exempt from compounds of nitrogen. At the end 
of this time analysis of the soil showed that while a small 
proportion of carbon (0.825° 1^) had wasted by oxidation, 
the quantity of nitrogen had slightly increased. The 
gain of nitrogen was but 0.009 grm. = 0.008"! o- 

In five other experiments where plants grew for several 
months in small quantities of the same garden soil, either 
in the free air but sheltered from rain and dew, or in a 
confined space and watered with pure water, analyses 



260 now CROPS feed. 

were made of the soil and seed before the trial, and of the 
soil and crop afterwards. 

The analyses show that while in all cases the plants 
gained some nitrogen beyond what was originally contain- 
ed in the seed, there was in no instance any loss of nitro- 
gen by the soil, and in three cases the soil contained more 
of this element after than before the trial. Here follow 
the results. 



No. of Exp. 


Weight of Crop, 
the seed taken as 1. 


Quantity of Soil. 


Gain of Nitrogen 






by plant. by soil. 


1. Lnpin,* 


3Ka 


130 grms. 


0.0042 grms. 0.0672 grms. 


2. Lupin, 


4 


130 '* 


0.0047 " 0.0081 " 


S. Hemp, 


5 


40 " 


0.0039 " 0.0000 " 


4. Bean, 


5 


50 " 


0.0226 " 0.0000 " 


B. Lupin,* 


3 


130 " 


0.0217 " 0.0454 " 



That the gain of nitrogen by the soil was not due to 
direct absorption of nitric acid or ammonia from the at- 
mosphere is demonstrated by the fact that it was largest 
in the two cases (Exps. 1 and 5) where the experiment was 
conducted in a closed vessel, containing throughout the 
whole time the same small volume, about 20 gallons, of 
air. 

In Exp. 4, where the soil at the conclusion contained no 
more nitrogen than at the commencement of the trial, it 
is scarcely to be doubted that the considerable gain of ni- 
trogen experienced by the plant came through the soil, 
and would have been found in the latter had it borne no 
crop. 

The experiments show that the quantity of nitrogen 
assimilated from the atmosphere by a given soil is very 
variable, or may even amount to nothing (Exp. 3); but 
they give us no clue to the circumstances or conditions 
which quantitatively influence the result. It must be ob- 
served that this fixation of nitrogen took place here in a 
soil very rich in organic matters, existing in the condition 
of humus, and capable of oxidation, so that the soil itself 

* Experiments made in confined air. 



THE NITEIC ACID OF THE SOIL. 261 

lost during three summer months eight-tenths of one per 
cent of carbon. In the numerous similar experiments 
made by Boussingault with soils destitute of organic mat- 
ter, no accumulation of nitrogen occurred beyond the 
merest traces coming from condensation of atmospheric 
ammonia. 

Certain experiments executed by Mulder more than 20 
years ago ( Che7nistry of Animal and Vegetable PJiysi' 
ology, p. 673) confirm the view we have taken. Two of 
these were " made with beans which had germinated in 
an atmosphere void of ammonia, and grown, in one case, 
in ulmic acid prepared from sugar, and also free from am- 
monia ; and, in the other case, in charcoal, both being 
moistened with distilled water free from ammonia. The 
ulmic acid and the charcoal were severally mixed up with 
1 per cent of wood ashes, to supply the plants with ash- 
ingredients. I determined the proportion of nitrogen in 
three beans, and also in the plants that were produced by 
three other beans. The results are as follows : — 

WMte beans in ubnic acid. Brown heaiis in charcoal. 

Weight. Nitrogen. Weight. Nitrogen. 

Beans, 1.465 grm. 50 cub. cent. 1.277 27 cub. cent. 

Plants, 4.167 " 160 " " 1.772 54 " 

The white beans, therefore, whilst growing into plants 
in substances and an atmosphere, both of which were free 
of ammonia, had obtained more than thrice the quantity 
of nitrogen that originally existed in the beans ; in the 
brown beans the original quantity was doubled." Mulder 
believed this experiment to furnish evidence that ammonia 
is produced by the union of atmospheric nitrogen with 
hydrogen set free in the decay of organic matters. To 
this notion allusion has been already made, and the con- 
viction expressed that no proof can be adduced in its 
favor (p. 239). The results of the experiments are fully 
explained by assuming that nitrogen was oxidized in nitri- 
fication, and no other explanation yet proposed accords 
with existincf facts. 



HOW CROPS FEED. 

As to the mode in which the soil thus assimilates free 
nitrogen, several hypotheses have been offered. One is 
that of Schonbein, to the effect that in the act of evapora- 
tion free nitrogen and water combine, with formation of 
nitrite of ammonia. In a former paragraph, p. 79, we 
have given the results of Zabelin, which appear to render 
this theory inadmissible. 

A second and adequate explanation is, that free nitrogen 
existing in the cavities of the soil is directly oxidized to 
nitric acid by ozone, which is generated in the action of 
ordinary oxygen on organic matters, (in the same way as 
happens when ordinary oxygen acts on phosphorus,) or is, 
perhaps, the result of electrical disturbance. 

Experiments by Lawes, Gilbert, and Pugh {Phil, 
Trans.^ 1861, II, 495), show indeed that organic matters 
in certain conditions of decay do not yield nitric acid 
under the influence of ozone. 

They caused air highly impregnated with ozone to pass 
daily for six months through moist mixtures of burned 
soil with relatively large quantities of saw-dust, starch, 
and bean meal, with and without lime — in all 10 mixtures 
— but in no case was any nitric acid produced. 

It would thus appear that ozone can form nitrates in 
the soil only when organic matters have passed into the 
comparatively stable condition of humus. 

That nitrogen is oxidized in the soil by ozone is highly 
probable, and in perfect analogy with what must happen 
in the atmosphere, and is demonstrated to occur in Schon- 
bein's experiments with moistened phosphorus (p. 66, 
also Ann, der Chem. u. Pharm.^ 89, 287), as well as in 
Zabelin's investigations that have been already recounted. 
(See pp. 75-83.) 

he fact, established by Keichardt and Blumtritt, that 
humus condenses atmospheric nitrogen in its pores (p. 
167), doubtless aids the oxidation of this element. 

The third mode of accounting for the oxidation of 



THE NITKIC ACID OF THE SOIL. 263 

free nitrogen is based upon the effects of a reducible 
body, like sesquioxide of iron or sulphate of lime, to 
which attention has been already directed. 

In a very carefully conducted experiment, Cloez * trans- 
mitted atmospheric air purified from suspended dust, and 
from nitric acid and ammonia, through a series of 10 large 
glass vessels filled with various porous materials. Vessel 
No. 1 contained fragments of unglazed porcelain ; 'No. 2, 
calcined pumice-stone ; N'o. 3, bits of well-Avashed brick. 
Each of these three vessels also contained 10 grms. of car- 
bonate of potash dissolved in water. The next three vessels, 
Nos. 4, 5, and 6, included the above-named porous materials 
in the same order ; but instead of carbonate of potash, they 
were impregnated Avith carbonate of lime by soaking in 
water, holding this compound in suspension. The vessel 
No. 7 was occupied with Meudon chalk, washed and 
dried. No. 8 contained a clayey soil thoroughly washed 
with water and ignited so as to carbonize the organic 
matters without baking the clay. No. 9 held the same 
earth washed and dried, but not calcined. Lastly, in No. 
10, was placed moist pumice-stone mixed with pure car- 
bonate of lime and 10 grms. of urea, the nitrogenous princi- 
ple of urine. Through these vessels a slow stream of puri- 
fied air, amounting to 160,000 liters, was passed, night and 
day, for 8 months. At the conclusion of the experiment, 
vessel No. 1 contained a minute quantity of nitric acid, 
which, undoubtedly, came from the atmosphere, having 
escaped the purifying apparatus. The contents of Nos. 
2, 4, and 5, were free from nitrates. Nos. 3 and 6, con- 
taining fragments of washed brick, gave notable evidences 
of nitric acid. Traces were also found in the washed 
chalk. No. 7, and in the calcined soil. No. 8. In No. 9, 
filled with washed soil, niter was abundant. No. 10, 



* Rechcrchcs sur la Nitrification— LeQons de Cliimie professtes en 1861 a la 
Soci6t6 Chimiquc do Paris, pp. 145-150. 



264 HOW CEOPS FEED. 

containing pumice, carbonate of lime, and urea, was desti- 
tute of nitrates. 

Experiments 2, 4, and 5, demonstrate that the concourse 
of nitrogen gas, a porous body, and an alkali-carbonate, 
is insufficient to produce nitrates. Experiment No. 10 
shows that the highly nitrogenous substance, urea,* dif- 
fused throughout an extremely porous medium and expos- 
ed to the action of the air in moist contact with carbonate 
of lime, does not suifer nitrification. In the brick (ves- 
sels JSTos. 3 and 6), something was obviously present, 
which determined the oxidation of free atmospheric ni- 
trogen. Cloez took the brick fresh from the kiln where 
it was burned, and assured himself that it included at 
the beginning of the experiment, no nitrogen in organic 
combination and no nitrates of any kind. Cloez believes 
the brick to have contained some oxidable mineral sub- 
stance, probably sulphide of iron. The Gentilly clay, 
used in making the brick, as well as some iron-cinder, 
added to it in the manufacture, furnished the elements of 
this compound. 

The slight nitrification that occurred in the vessels 
Nos. 7 and 8, containing washed chalk and burned soil, 
likewise points to the oxidizing action of some mineral 
matter. In vessel ISTo. 9, the simply washed soil, which 
was thus freed from nitrates before the trial began, un- 
derwent a decided nitrification in remarkable contrast to 
the same soil calcined (No. 8). The influence of humus 
is thus brought out in a striking manner. 

It may be that apocrenic acid, which readily yields 
oxygen to oxidable matters, is an important agent in 



Urea (COH4 Na) contains in 100 parts : 

Carbon, 20.00 
Hydrogen, G.G7 
Nitrogen, 46.67 
Oxygen, 26. 6G 

lOO.OQ 



THE NITKIC ACID OF THE SOIL. 265 

nitrification. As we have seen, this acid, according to 
Mulder, passes into crenic acid by loss of oxygen, to he 
reproduced from the latter by absorption of free oxygen. 
The apocrenate of sesquioxide of iron, in which both acid 
and base are susceptible of this transfer of oxygen, 
should thus exert great oxidizing power. (See p. 228.) 

The Conditions Influencing Nitrification have been 
for the most part already mentioned incidentally. We 
may, however, advantageously recapitulate them. 

a. The formation of nitrates appears to require or to be 
facilitated by an elevated temperature^ and goes on most 
rapidly in hot weather and in hot climates. 

h. According to Knop, ammonia that has been absorbed 
by a soil suffers no change so long as the soil is dry ; but 
when the soil is moistened, nitrification quickly ensues. 
Water thus appears to be indispensable in this process. 

c. An alkali base or carbonate appears to be essential 
for the nitric acid to combine with. It has been thought 
that the mere presence of potash, soda, and lime, favors 
nitrification, " disposes," as is said, nitrogen to unite with 
oxygen. Boussingault found, however {Chimie Agri- 
cole^ III, 198), that caustic lime developed ammonia from 
the organic matters of his garden soil without favoring 
nitrification as much as mere sand. The caustic lime by 
its chemical action, in fact, opposed nitrification ; while 
pure sand, probably by dividing the particles of earth and 
thus perfecting their exposure to the air, facilitated this 
process. Boussingault' s experiments on this point were 
made by inclosing an earth of known composition (from his 
garden) with sand, etc., in a large glass vessel, and, after 
three to seven months, analyzing the mixtures, which were 
made suitably moist at the outset. Below are the results 
of five experiments. 

I. 1000 grms. of soil and S50 grms. eaud acquired 0.012 grms. ammonia and 
0.482 grms. nitric acid. 

II. 1000 grms. of soil and 5500 grms. sand acquired 0.035 grms. ammonia and 
0.545 grms. nitric acid. 

12 



266 HOW CKOPS FEED. 

III. 1000 grms. of soil and 500 grms, marl acquired 0.002 grms. ammonia and 
0.360 grms. nitric acid. 

IV. 1000 grms. of soil and 2 grms. carbonate of potash acquired 0.015 grms. 
ammonia and 0.290 grms. nitric acid. 

v. 1000 grms. of soil and 200 grms. quicklime acquired 0.303 grms. ammonia 
and 0.099 grms. nitric acid. 

The unfavorable eifect of caustic lime is well pronounc- 
ed and is confirmed by other similar experiments. Car- 
bonate of potash, which is strongly alkaline, but was used 
in small quantity, and marl (carbonate of lime), which is 
but very feebly alkaline, are plainly inferior to sand in 
their influence on the development of nitric acid. 

The effect of lime or carbonate of potash in these ex- 
periments of Boussingault may, perhaps, be thus explain- 
ed. Many organic bodies which are comparatively stable 
of themselves, absorb oxygen with great avidity in pres- 
ence of, or rather when combined with, a caustic alkali. 
Crenic acid is of this kind ; also gallic acid (derived from 
nut-galls), and especially pyrogallic acid (a result of the 
dry distillation of gallic acid). The last-named body, 
when dissolved in potash, almost instantly removes the 
oxygen from a limited volume of air, and is hence used 
for analysis of the atmosphere.* 

We reason, then, that certain organic matters in the 
soil of Boussingault's garden, became so altered by treat- 
ment with lime or carbonate of potash as to be susceptible 
of a rapid oxidation, in a manner analogous to what hap- 
pens with pyrogallic acid. Dr. R. Angus Smith has shown 
(Jour. Boy. Ag. JSoc, XVII, 436) that if a soil rich in or- 
ganic matter be made alkaline, moist, and warm, putre- 
factive decomposition may shortly set in. This is what 
happens in every well-managed compost of lime and j^eat. 
By this rapid alteration of organic matters, as Ave shall see 
(p. 268), not only is nitric acid not formed, but nitrates 
added are reduced to ammonia. It is not improbable that 



* Not all organic bodies, by any means, are thus affected. Lime hindeT'S the 
alteration of urine, flesh, and the albuminoids. 



THE laTEIC ACID OF THE SOIL. 26T 

smaller doses of lime or alkali than those employed by 
Boussingault would have been found promotive of nitri- 
fication, especially after the lapse of time sufficient to 
allow the first rapid decomposition to subside, for then 
we should expect that its presence would favor slow oxida- 
tion. This view is in accordance with the idea, universally 
received, that lime, or alkali of some sort, is an indispensa- 
ble ingredient of artificial niter-beds. The point is one 
upon which further investigations are needed. 

d. Free, oxygen^ i. e., atmospheric air, and the porosity 
of soil which ensures its contact with the particles of the 
latter, are indispensable to nitrification, which is in all 
cases a process of oxidation. When sesquioxide of iron 
oxidizes organic matters, its action would cease as soon as 
its reduction to protoxide is complete, but for the atmos- 
pheric oxygen, which at once combines with the protoxide, 
constantly reproducing the sesquioxide. 

In the saltpeter plantations it is a matter of experience 
that light, porous soils yield the largest product. The 
operations of tillage, which promote access of air to the 
deeper portions of earth- and counteract the tendency of 
many soils to " cake " to a comparatively impervious mass, 
must also favor the formation of nitrates. . 

Many authors, especially Mulder, insist upon the physic- 
al influence of porosity in determining nitrification by 
condensed oxygen. The probability that porosity may 
assist this process where compounds of nitrogen are con- 
cerned, is indeed great ; but there is no evidence that any 
porous body can determine the union of free nitrogen and 
oxygen. Knop found that of all the proximate ingredi- 
ents of the soil, clay alone can be shown to be capable of 
physically condensing gaseous ammonia (humus combines 
with it chemically, and if it previously efiects physical 
condensation, the fact cannot be demonstrated). 

The observations by Reichardt and Blumtritt on the 
condensinor effect of the soil for the erases of the atmos- 



268 HOW CKOPS PEED. 

phere (p. 167) indicate absorption both of oxygen and 
nitrogen, as well as of carbonic acid. The fact that char- 
coal acts as an energetic oxidizer of organic matters has 
been alluded to (p. 169). This action is something very- 
remarkable, although charcoal condenses oxygen but to a 
slight extent. The soil exercises a similar but less vigorous 
oxidizing effect, as the author is convinced from experi- 
ments made under his direction (by J. J. Matthias, Esq.), 
and as is to be inferred from the well-known fact that the 
odor of i^utrefying flesh, etc., cannot pass a certain thickness 
of soil. But charcoal is unable to accomplish the union 
of oxygen and nitrogen at common temperatures, or at 
212° F., either dry, moistened with pure water, or with 
solution of caustic soda. (Experiments in Sheffield labo- 
ratory, by Dr. L. H. Wood.) 

Putrefying flesh, covered with charcoal as in Stenhouse's 
experiment (p. 169) gives off ammonia, but no nitric acid is 
formed. Dumas has indeed stated ( Cojnptes Bend.^ XXIII) 
that ammonia mixed with air is converted into nitric 
acid by a porous body — chalk — that has been drenched 
with caustic potash and is heated to 212° F. But this is 
an error, as Dr. Wood has demonstrated. It is true that 
platinum at a high temperature causes ammonia and oxy- 
gen to unite. Even a platinum wire when heated to red- 
ness exerts this effect in a striking manner (Kraut, A7m, 
Ch. u. Ph., 136, 69) ; but spongy platinum is without ef- 
fect on a mixture of air and ammonia gas at 212° or lower 
temperatures. (Wood.) 

e. Presence of organic matters prone to oxidation. Re- 
duction of nitrates to ammonia, etc., in the soil. — As we 
have seen, the organic matters (humus) of the soil are a 
source of nitric acid. But it appears that this is not al- 
ways or universally true. In compact soils, at a certain 
depth, organic matters (their liydrogen and carbon) may 
oxidize at the expense of nitric acid itself, converting the 
latter into ammonia. Pelouze {Comptes Pendus, XLIV, 



THE NITRIC ACID OF THE SOIL. 269 

118) has proved that putrefying animal substances, as al- 
bumin, thus reduce nitric acid with formation of ammonia. 
For this reason, he adds, the liquor of dung heaps and 
putrid urine contains little or no nitrates. Boussingault 
{Agronomie^ II, 17) examined a remarkably rich alluvial 
soil from the junction of the Amazon with the Rio Cupari, 
made up of alternate layers of sand and partially decayed 
leaves, containing 40° 1^ of the latter. This natural leaf- 
compost contained no trace of nitrates, but an exception- 
ally high quantity of ammonia, viz., .05° |^^. 

Kuhlmann {A^in. de Chim. et de JPhys.^ 3 Ser., XX) 
was the first to draw attention to the probability that ni- 
tric acid may thus be deoxidized in the lower strata of 
the soil, and his arguments, drawn from facts observed 
in the laboratory, appear to apply in cases where there 
exist much organic matters and imperfect access of air. 
In a soil so porous as is demanded for the culture of most 
crops these conditions cannot usually occur, as Grouven 
has taken the trouble to demonstrate (Zeitschrift far 
Deutsche JLandwirthe^ 1855, p. 341). In rice swamps and 
peat bogs, as well as in wet compost heaps, this reduction 
must proceed to a considerable extent. 

In some, if not all cases, the addition of much lime or 
other alkaline substance to a soil rich in organic matters 
sets up rapid putrefactive decomposition, whereby nitrates 
are at once reduced to ammonia (p. 266). 

In one and the same soil the conditions may exist at 
different times that favor nitrification on the one hand, 
and reduction of nitrates to ammonia on the other. A 
surplus of moisture might so exclude air from a porous 
soil as to cause reduction to take place, to be succeeded 
by rapid nitrification as the soil becomes more dry. 

It is possible that nitrates may undergo further chemi- 
cal alteration in the presence of excess of organic matters. 
That nitrites may often exist in the soil is evident from 
what has been written with res^ard to the mutual convert- 



S70 HOW CROPS PEED. 

ibility of nitrates and nitrites (p. 73). According to 
Goppelsroder {Dingier' s Polytech. Jour.^ 164, 388), certain 
soils rich in humus possess in a high degree the power to 
reduce nitrates to nitrites. It is not unlikely that further 
reduction may occur — that, in fact, the deoxidation may 
be comj^lete and free nitrogen be disengaged. This is a 
question eminently worthy of study. 

Loss of IVitratcs may occur when the soil is saturated 
with water, so that the latter actually flows through and 
away from it, as hapj^ens during heavy rains, the nitrates 
(those of sesquioxide of iron, perha23s, excepted) being 
freely soluble and not retained by the soil. Boussingault 
made 40 analyses of lake and river water, 25 of spring 
water, and 35 of well water, and found nitric acid in ev- 
ery case, though the quantity varied greatly, being largest 
in cities and fertile regions. Thus the w^ater of the upper 
Rhine contains one millionth, that of the Seine, in Paris, 
six millionth s, and that of the Nile four millionth s of ni- 
tric acid. The Rhine daily removes from the country 
supplying its waters an amount of nitric acid equivalent 
to 220 tons of saltpeter. The Seine carries daily into the 
Atlantic 270 tons, and the Nile pours 1,100 tons into the 
Mediterranean every twenty-four hours. 

In the wells of crowded cities the proportion of nitrates 
is much higher. In the older parts of Paris the well wa- 
ters contain as much as one part of niter (or its equiva- 
lent of other nitrates) in 500 of water. 

The soil may experience a loss of nitrates by the com- 
plete reduction of nitric acid to gaseous nitrogen, or by 
the formation of inert compounds with humus, as will be 
noticed in the next section. 

Loss of assimilable nitrogen by the washing of nitrates 
from the soil may be hindered to some extent in compact 
soils by the fact just noticed that nitric acid is liable to be 
converted into ammonia, which is at once rendered com- 
paratively insoluble. 



THE NITEIC ACID OF THE SOIL. 



271 



Mtric Acid as Food to Plants. — Experiments demon- 
strating that nitric acid is capable of perfectly supplying 

vegetation with 
nitrogen were 
first made by 
Boiiss i n g a u 1 1 
{Agronomie^ 
Chimle -Agrl- 
cole, etc., 1,210). 
We give an ac- 
count of some 
of these. 

Two seeds of 
a dwarf Sunflow- 
er (Ilelianthus 
argo]yhyllus), 
were planted in 
each of three 
pots, the soil of 
which, consist- 
ing of a mixture 
of brick - dust 
and sand, as well 
as the pots them- 
selves, had been, 
thoroughly 
freed from all ni- 
trogenous com- 
pounds by igni- 
tion and wash- 
ing: with distill- 
Fig. 9. ed water. To 

the soil of the pot A, fig. 9, nothing was added save the 
two seeds, and distilled water, with which all the plants 
were watered from time to time. With the soil of pot 
C, were incorporated small quantities of phosphate of lime, 




272 



HOW CROPS FEED. 



of ashes of clover, and bicarbonate of potash, in order that 
the plants growing in it might have an abundant supply 
of all the ash-ingredients they needed. Finally, the soil 
of pot D received the same mineral matters as pot C, and, 
in addition, a small quantity (1.4 gram) of nitrate of pot- 
ash. The seeds were sown on the 5th of July, and on the 
oOth of September, the plants had the relative size and 
appearance seen in the figure, where they are represented 
in one-eighth of the natural dimensions. 

For the sake of comparison, the size of one of the 
largest leaves of the same kind of Sunflower that grew 
in the garden is represented at D, in one-eighth of its 
natural dimensions. 

Nothing can be more striking than the influence of the 
nitrate on the growth of this plant, as exhibited in this 
experiment. The plants A and C are mere dwarfs, al- 
though both carry small and imperfectly developed flow- 
ers. The plant D, on the contrary, is scarcely smaller 
than the same kind of plant growing under the best con- 
ditions of garden culture. Here follows a Table of the 
results obtained by the examination of the plants. 





ill 


■§1 
II 
11 


i 


Acquired by tJie 

plants in 86 days 

of vegetation. 


• 


Carbon. 


Nitro- 
gen. 


A— nothing added to the soil 


3.6 


grm. 
0.285 


cubic 

cent. 

2.45 


grm. 
0.114 


grm. 
0023 






C— ashes, phosphate of lime, and bi- 
carbonate of potash, added to the 
soil 


4.6 


0.391 


3.42 


0.156 


0.0027 


D— ashes, phosphate of lime, and ni- 
trate of potash, added to tlie soil.. 


198.3 


21.111 


182.00 


8.444 


0.1666 



"We gather from the above data : 

1. That without some compound of nitrogen in the soil 
vegetation cannot attain any considerable development, 
notwithstanding all requisite ash-ingredients are present 



THE NITRIC ACID OF THE SOIL. 



273 



in abundance. Observe that in exps. A and C the crop 
attained but 4 to 5 times greater weight than the seed, 
and gathered from the atmosphere during 86 days but 2^ 
milligrams of nitrogen. The crop, supplied with nitrate 
of potash, weighed 200 times as much as the seed, and 
assimilated 66 thnes as much nitrogen as was acquired by 
A and C from external sources. 

2. That nitric acid of itself may furnish all the nitrogen 
requisite to a normal vegetation. 

In another series of experiments (Agronomie, etc., I, pp. 
227-233) Boussingault prepared four pots, each containing 
145 grains (about 5 oz. avou'dupois) of calcined sand 
with a little phosphate of lime and ashes of stable-dung, 
and planted in each two Sunflower seeds. To three of 
the pots he added weighed quantities of nitrate of soda — 
to No. 3 twice as much as to No. 2, and to No. 4 three 
times as much as to No. 3 ; No. 1 received no nitrate. 
The seeds germinated duly, and the plants, sheltered from 
rain and dew, but fully exposed to air, and watered with 
water exempt from ammonia, grew for 50 days. In the 
subjoined Table is a summary of the results. 







Co 


& 




-IS . 


Wd 


'^^S 


1 


* 


^1 


i 






1 tS 


Relative weights 
matter organizt 
that of first Ea 
taken as unity. 


Relative weights 
N. at disposal 
crops., that of 
first Exp. taken 
unity. 




grms. 


grms. 


grms. 


grms. 


grms. 


grms. 


grms. 


grms. 


1.. 0.0038 


0.0000 


0.0033 


0.0053 


0.0020t 


0.397 


1 


1 





0033 


0.0033 


0.0006 


0.0063 


0.00021: 


0.720 


1.8 


2 


^ 


0033 


0.0066 


0.0099 


0.0097 


0.0002; 


1.130 


2.8 




4.. 


0.0033 


0.0264 


0.0297 


0.0251 


0.0046t 


3.280 


8.5 1 y 



* N=Nitrogen. 



In the first Exp. a trifling quantity of nitrogen was 
gathered (as ammonia?) from the air. In the others, and 
especially in the last, nitrate of soda remained in the soil, 
12* 



274 HOW CROPS FEED. 

not having been absorbed entirely by the plants. Observe, 
however, what a remarkable coincidence exists between 
the ratios of supply of nitrogen in form of a nitrate and 
those of growth of the several crops, as exhibited in the 
last two columns of the Table. IS'othing could demon- 
strate more strikingly the nutritive function of nitric acid 
than these admirable investigations. 

Of the multitude of experiments on vegetable nutrition 
which have been recently made by the process of water- 
culture {JU. C. G., p. 167), nearly all have depended upon 
nitric acid as the exclusive source of nitrogen, and it has 
proved in all cases not only adequate to this purpose, but 
far more certain in its effects than ammonia or any other 
nitrogenous compound. 



§6. 

NITROGENOUS ORGANIC MATTERS OF THE SOIL. 

AVAILABLE NITROGEN.— QUANTITY OF NITROGEN 
REQUIRED FOR CROPS. 

In the minerals and rocks of the earth's surface nitrogen 
is a very small, scarcely appreciable ingredient. So far as 
we now know, ammonia-salts and nitrates (nitrites) are 
the only mineral compounds of nitrogen fOund in soils. 
When, however, organic matters are altered to humus, 
and become a part of the soil, its content of nitrogen ac- 
quires significance. In peat, which is humus compara- 
tively free from earthy matters, the proportion of nitrogen 
is often very considerable. In 32 specimens of peat ex- 
amined by the author (I^eat and its Uses as Fertilizer and 
Fuel^ p. 90), the nitrogen, calculated on the organic mat- 
ters^ ranged from 1.12 to 4.31 per cent, the average being 
2.6 per cent. The average amount of nitrogen in the air- 
dry and in some cases highly impure peat, was 1.4 per 
cent. This nitrogen belongs to the organic matters in 



NITFvOGENOUS ORGANIC MATTERS OF THE SOIL. <iiO 

great part, but a small proportion of it being in the form 
of ammonia-salts or nitrates. 

In 1846, Krocker, in Liebig's laboratory, first estimated 
the nitrogen in a number of soils and marls {Ann. Ch. it. 
Ph., 58, 387). Ten soils, whicli were of a clayey or loamy 
character, yielded from 0.11 to 0.14 per cent; three sands 
gave from 0.025 to 0.074 per cent ; seven marls contained 
0.004 to 0.083 per cent. 

Numerous examinations have since been made by An- 
derson, Liebig, Ritthausen, Wolff, and others, with simi- 
lar results. 

In all but his latest writings, Liebig has regarded this 
nitrogen as available to vegetation, and in fact designated 
it as "ammonia. Way, Wolff, and others, have made evi- 
dent that a large portion of it exists in organic combina- 
tion. Boussingault {Agronomie, T. I) has investigated 
the subject most fully, and has shown that in rich and 
highly manured soils nitrogen accumulates in considerable 
quantity, but exists for the most part in an insoluble and 
inert form. In the garden of Liebfrauenberg, which had 
been heavily manured for centuries, but 4''|„ of the total 
nitrogen existed as ammonia-salts and nitrates. The soil 
itself contained — 

Total nitrogen, 0.261 per cent. 
Ammonia, 0.0022 " " 

Nitric acid, 0.00034 " " 
The subjoined Table includes the results of Boussin- 
gault's examinations of a number of soils from France and 
South America, in which are given the quantities of am- 
monia, of nitric acid, expressed as nitrate of potash, and 
of nitrogen in organic combination. These quantities are 
stated both in per cent of the air-dry soil, and in lbs. av. 
per acre, taken to the depth of 17 inches. In another 
column is also given the ratio of nitrogen to carbon in the 
organic matters. {Agronomle, T II, pp. 14-21.) 



276 



HOW CKOPS FEED. 



Ammonia, Nitrates, .cJTd Organic Nitkogen 


OF VATvIOTJS 


Soils 






Ammonia. 


mtrate of 
potash. 


JSitrogen in 
org. combVn. 




Soils. 




lbs. 




lbs. 




lbs 


O^-KJ , 




per 


per 


per 


per 


per 


per 


~ ^-"S 




cent. 


acre 


cent 


acre 


cent. 


acre 


(^le 


^ fLiebfrauenbcrg, lightgard. soil 


0.0022 


100 


0.0175* 


875 


0.259 


12970 


1:9.3 


g J Bischwiller, light garden soil... 


0.0020 


100 


0.1526 


7630 


0.295 


14755 


1:9.7 


c3 j Bechelbronn, wheat field clay. 


0.0009 


45 


0.0015 


75 


0.139 


6985 


1:8.2 


^ [ Argentan, rich pasture 


0.0060 


300 


0.004G 


230 


0.513 


256501 1:8 


rt fHio Madeira, sugar field, clay 


0.0000 


450 


0.0004 


20 


0.143 


7140 1:6.3 


,^ Itio Trombetto, forest heavy do. 


0.0030 


183 


0.0001 


5 


0.119 


5955 


1:4.9 


53 1 Rio Negro, prairie v. fine sand. 


0.003S 


190 


0.0001 


51 


0.068 


3440 


1:5.6 


£ J Santarem, cocoa plantation.. 
< 1 Saracca, near Amazon, loam... 


0.0083 


415 


0.0011 


551 


0.G49 


32450 


1:11 


0.0042 


210 


none 


0.182 


9100 


1:8.2 


r2 Rio Cupari, rich leaf mould. . . . 


0.0525 


28T5 




0.685 


34250 


1:18.8 


g lies du Salut, French Guiana... 


O.OOSO 


400 


0.0643 3215 


0.543 


27170 


1:11.7 


cc [Martinique, sugar field 


0.0055 


275! 


0.0186 930 


0.112 


5590 


1:8 



* The same soil whose partial analysis has just been given, but examined for 
nitrates at another time. 

It is seen that in all cases the nitrogen in the forms of 
ammonia f and nitrates | is much less than that in organic 
combination, and in most cases, as in the Liebfrauenberg 
garden, the disparity is very great. 

Nature of the Nitrogenous Organic Matters. Amides. 

— Hitherto we have followed Mulder in assuming that the 
humic, ulmic, crenic, and apocrenic acids, are destitute of 
nitrogen. Certain it is, however, that natural humus is 
never destitute of nitrogen, and, as we have remarked in 
case of peat, contains this element in considerable quanti- 
ty, often 3 per cent or more. Mulder teaches that the 
acids of humus, themselves free from nitrogen, are nat- 
urally combined to ammonia, but that this ammonia is 
with difficulty expelled from them, or is indeed impossible to 
separate completely by the action of solutions of the fixed 
alkalies. In all chemistry, beside, there is no example 
of such a deportment, and we may well doubt whether 
the ammonia that is slowly evolved when natural humus 
is boiled with potash is thus expelled from a humate of 
ammonia. It is more accordant with general analogies to 



+ Ammonia contains 82.4 per cent of nitrogen. 

X Nitrate of potash contains 13.8 per cent of nitrogen. 



NIIEOGENOUS ORGANIC MATTERS OF THE SOIL. 277 

suppose that it is generated by the action of the alkali. 
In fact, there are a large number of bodies which manifest 
a similar deportment. Many substances which are pro- 
duced from ammonia-compounds by heat and otherwise, 
and called amides^ to which allusion has been already 
made, p. 276, are of this kind. Oxalate of ammonia, when 
heated to decomposition, yields oxamide, which contains 
the elements of the oxalate minus the elements of two 
molecules of water, viz., 

Oxalate of ammonia, Oxamide. Water. 

2 (N HJ C, O, = 2 (^ HJ C, O, + 2 H,0 

On boiling oxamide with solution of potash, ammonia 
is reproduced by the taking up of two molecules of water, 
and passes off as a gas, Avhile oxalate of potash remains in 
the liquid. 

JSTearly every organic acid known has one or several 
amides, bearing to it a relation similar to that thus sub- 
sisting between oxalic acid and oxamide. 

Asparagine, a crystallizable body found in asparagus 
and many other plants, already mentioned as an amide, is 
thought to be an amide of malic acid. 

Urea, the principal solid ingredient of human urine, is 
an amide of carbonic acid. Uric acid, hippuric acid, gua- 
nine, found also in urine ; kreatin and kreatinine, occurring 
in the juice of flesh ; thein, the active principle of tea and 
coffee ; and theobromin, that of chocolate, are all regard- 
ed as amides. 

Amide-like boaies are gelatine (glue), the organic sub- 
stance of the tendons and of bones, that of skin, hair, 
wool, and horn. The albuminoids themselves are amide- 
like, in so far that they yield ammonia on heating with 
solutions of caustic alkalies. 

Albuminoids a Source of the Nitrogen of Humus.— 

The organic nitrogen of humus may come from the albu- 
minoids of the vegetation that has decayed upon or in the 



278 HOW CROPS FEED. 

soil. In their alteration by decay, a portion of nitrogen 
assumes the gaseous form, but a portion remains in an in- 
soluble and comparatively unalterable condition, though 
in what particular compounds we are unable to say. The 
loss of carbon and hydrogen from decayiiig organic mat- 
ters, it is believed, usually proceeds more rapidly than the 
waste of nitrogen, so that in humus, which is the residue 
of the change, the relative proportion of nitrogen to car- 
bon is greater than in the original vegetation. 

Reyersion of Nitric Acid and Ammonia to inert Forms. 
— It is probable that the nitrogen of ammonia, and of ni- 
trates, which are reducible to ammonia under certain con- 
ditions, may pass into organic combination in the soil. 
Knop ( Yersuchs St., Ill, 228) found that when peat or 
soils containing humus were kept for several months in 
contact with ammonia in closed vessels, at the usual tem- 
perature of summer, the ammonia, according to its quan- 
tity, completely or in part disappeared. There having been 
no such amount of oxygen present as would be necessary to 
convert it into nitric acid, the only explanation is that the 
ammonia combined with some organic substance in the 
humus, forming an amide-like body, not decomposable by 
the hypochlorite of soda used in Knop's azometrical anal- 
ysis. 

Facts supporting the above view by analogy are not 
wanting. When gelatine (a body of animal origin closely 
related to the albuminoids, but containing 18 instead of 
15" |„ of nitrogen) is boiled with dilute acids for some 
time, it yields, among other products, sugar, as Gerhardt 
has demonstrated. Prof T. Sterry Hunt was the first to 
suggest {Am. Jour. Sci. S Arts, 1848, Vol. 5, p. 76) that 
gelatine has nearly the composition of an amide of dextrin 
or other body of the cellulose group, and might be regard- 
ed as derived chemically from dextrin (or starch) by the 
union of the latter with ammonia, water being eliminated, 
viz.: 



NITEOGENOUS ORGANIC MATTERS OF THE SOIL. 279 

Carbohydrate. Ammonia. Water. Gelatine. 

C„ H,. O.. + 4 NH, = 6 HP + 2 (C, H,. N, O,). 

Afterwards Dusart, Schiitzenberger, and P. Thenard, in- 
dependently of each other, obtamed by exposing dextrin, 
starch, and glucose, to a somewhat elevated temperature 
(300-360°F.), in contact with ammonia-water, substances 
contaming from 11 to 19° [^ of nitrogen, some soluble in 
water and having properties not unlike those of gelatine, 
others insoluble. It was observed, also, that analogous 
compounds, containing less nitrogen, were formed at lower 
temperatures, as at 212° F. Payen had previously observed 
that cane sugar underwent entire alteration by prolonged 
action of ammonia at common temperatures. 

These facts scarcely leave room to doubt that ammonia, 
as carbonate, by prolonged contact with the humic acids 
or with cellulose, and bodies of like composition, may 
form combinations with them, from which, by the action 
of alkalies or lime, ammonia may be regenerated. 

It has already been mentioned that when soils are boil- 
ed with solutions of potash, they yield ammonia continu- 
ously for a long time. 

Boussingault observed, as has been previously remarked, 
that lime, when incorporated with the soil at the ordinary 
temperature, causes its content of ammonia to increase. 

Soil from the Liebfrauenberg garden, mixed with ^|^ 
its weight of lime and nearly \ its weight of water, was 
placed in a confined atmosphere for 8 months. On open- 
ing the vessel, a distinct odor of ammonia was perceptible, 
and the earth, wbich originally contained per kilogram, 
11 milligrams of this substance, yielded by analysis 303 
mgr. (See p. 265, for other similar results.) 

Alteration of AlbuMinoids in the Soil.— Albuminoids 
are carried into the soil when fresh vegetable matter is in- 
corporated with it. They are so susceptible to alteration, 
however, that under ordinary conditions they must speed- 



280 HOW CEOPS FEED. 

ily decompose, and cannot therefore themselves be consid- 
ered as ingredients of the soil. 

Among the proximate products of their decomposition 
are organic acids (butyric, valeric, propionic) destitute of 
nitrogen, and the amides leucin (Cg H^g NOJ and tyrosin 
(Cg Hjj NO3). These latter bodies, by further decompo- 
sition, yield ammonia. As has been remarked, it is proba- 
ble that the albuminoids, when associated as they are in 
decay with cellulose and other carbohydrates, may at 
once give rise to insoluble amide-like bodies, such as those 
whose existence in humus is evident from the consider- 
ations already advanced. 

Can these Organic Bodies Yield Nitrogen Directly to 
Plants ? — Those nitrogenous organic compounds that exist 
in the soil associated with humus, which possess something 
of the nature of amides, though unknown to us in a pure 
state, appear to be nearly or entirely incapable of feeding 
vegetation directly. Our information on this point is de- 
rived from the researches of Boussingault, whose papers 
on this subject [De la Terre vegetale consider ee dans ses 
effets sur la Vegetatioii) are to be found in his Agronomic^ 
etc., Vols. I and II. 

Boussingault experimented with the extremely fertile 
soil of his garden, which was rich in all the elements 
needful to support vegetation, as was demonstrated by the 
results of actual garden culture. This soil was especially 
rich in nitrogen, containing of this element 0.26" |„, which, 
were it in the form of ammonia, would be equivalent to 
more than 7 tons per acre taken to the depth of 13 inches ; 
or, if existing as nitric acid, would correspond to more 
than 43 tons of saltpeter to the acre taken to the depth 
just mentioned. 

This soil, however, when employed in quantities of 40 
to 130 grams (1^ to 4|- oz. av.) and shielded from rain 
and dew, was scarcely more capable of carrying lupins, 
beans, maize, or hemp, to any considerable development, 



AVAILABLE NITROGEN OF THE SOIL. 281 

than the most barren sand. In eight distinct trials the 
crops Treighed (dry) but 3 to 5 times, in one case 8 times 
(average 4 times), as much as the seed; while in sand, 
pumice, or burned soil, containing no nitrogen, Boussin- 
gault several times realized a crop weighing 6 times as 
much as the seed, though the average croj) of 38 experi- 
ments was but 3 times, and the lowest result 1^ times the 
weight of the seed. 

The fact that the nitrogen of this garden soil was for 
the most j^ai't inert is strikingly shown on a comparison 
of the crops yielded by it to those obtained in barren 
soil with aid of known quantities of nitrates. 

In a series of experiments with the Sunflower, Boussin- 
gault {Agronomie^ etc.^ I, p. 233) obtained in a soil desti- 
tute of nitrogen a crop weighing (dry) 4.6 times as much 
as the seeds, the latter furnishing the j^lants 0.0033 grm. of 
nitrogen. In a second pot, with same weight of seeds, in 
which the nitrogen was doubled by adding 0.0033 grm. in 
form of nitrate of soda, the weight of crop was nearly 
doubled — was 7.6 times that of seeds. In a third pot the 
nitrogen was trebled by adding 0.0066 grm. in form of ni- 
trate, and the crop was nearly trebled also — was 11.3 
times the weight of the seeds. 

In another experiment (p. 271) the addition of 0.194 
grm. of nitrogen as nitrate of potash to barren sand with 
needful mineral matters, gave a croj) weighing 198 times 
as much as the seeds. But in the garden soil, which con- 
tained, when 40 grms. were employed 0.104 grm., and when 
130 grms. were used 0.338 grm. of nitrogen, the result of 
growth was often not greater than in a soil that contained 
'no nitrogen, and only in a single instance surpassed that 
of a soil to which was added but 0.0033 grm. The fact 
is thus demonstrated that but a very small proportion of 
the nitrogen of this soil was assimilable to vegetation. 

From these beautiful investigations Boussingault deems 
it highly probable that in this garden soil, and in soils 



282 HOW CROPS FEED. 

generally which have not been recently manured, ammonia 
and nitric acid are the exclusive feeders of vegetation with 
nitrogen. Such a view is not indeed absolutely demon- 
strated, but the experiments alluded to render it in the 
highest degree probable, and justify us in designating the 
organic nitrogen for the most part as inert, so far as vege- 
table nutrition is concerned, until altered to nitrates or 
ammonia-salts by chemical change. 

To comprehend the favorable results of garden-culture 
in such a soil, it must be considered what a large quantity 
of earth is at the disposal of the crop, viz., as Bous^ingault 
ascertained, 57 lbs. for each hill of dwarf beans, 190 lbs. 
for each hill of potatoes, 470 lbs. for each tobacco plant, 
and 2,900 lbs. for every three hop-plants. 

The quantity and condition of the nitrogen of Boussin- 
gault's garden soil are stated in the subjoined scheme. 

Available ( Ammonia 0.00220 per cent = Nitrogen 0.00181 per cent I n nmo r^or nt 
nitrogen "[ Nitric acid 0.00034 " " = " 0.00009 " " |-u.uuiJ per ct. 
Inert nitrogen— of organic compounds 0.2591 " " 

Total nitrogen 0.2610 per ct. 

Calculation shows that in garden culture the plants 
above named would have at their disposal in this soil quan- 
tities of inert and available nitrosren as follows : 



Weight of soil. 

Bean (dwarO hill 57 lbs. 
Potato, " 190 " 
Tobacco, single plant, 470 " 
Hop, three plants, 2900 " 


Ine7't nitrogen. 

75 grams.* 
242 " 
555 " 
3438 " 

nearly. 


Available 
nitrogen. 
Igram. 
3 grams. 
7 " 
44 " 


* 1 gram =z 15 grains avoirdupois 
17 grams = 1 oz. " 





283 " = lib. 

Indirect Feeding of Crops by the Organic Nitrogen 
of the Soil. — In what has been said of the oxidation of 
the organic matters of the soil, (whereby it is probable 
that their nitrogen is partially converted into nitric acid,) 
and of the effect of alkalies and lime upon them, (whereby 
ammonia is generated,) is given a clue to the understand- 



AVAILABLE NITROGEN OF THE SOIL. 283 

ing of their indirect nutritive influence upon vegetation. 
By these chemical transformations the organic nitrogen 
may pass into the two compounds which, in the present 
state of knowledge, we must regard as practically the ex- 
clusive feeders of the plant with nitrogen. The rapidity 
and completeness of the transformation depend upon 
circumstances or conditions which we understand but im- 
perfectly, and which are extremely important subjects for 
further investigation. 

Difficulty of estimating the Available Nitrogen of any 
Soil. — The value of a soil as to its power of supplying 
plants with nitrogen is a problem by no means easy to 
solve. The calculations that have just been made from 
the analytical data of Boussingault regarding the soil of 
his garden are necessarily based on the assumption that 
no alteration in the condition of the nitrogen could take 
place during the j^eriod of growth. In reality, however, 
there is no constancy either in the absolute quantity of 
nitrogen in the soil or in its state of availability. Por- 
tions of nitrogen, both from the air and from fertilizers, 
may continually enter the soil and assume temporarily the 
form of insoluble and inert organic combinations. Other 
portions, again, at the same time and as continually, may 
escape from this condition and be washed out or gathered 
by vegetation in the form of soluble nitrates, as has al- 
ready been set forth. It is then manifestly impossible to 
learn more from analysis, than how much nitrogen is avail- 
able to vegetation at the moment the sample is examined. 
To estimate with accuracy wdiat is assimilable during the 
whole season of growth is simply out of the question. 
The nearest approach that can be made to this result is to 
ascertain how much a crop can gather from a limited vol- 
ume of the soil. 

Bretschneider's Experiments. — We may introduce liere 
a notice of some recent researches made by Bretschneider 
in Silesia, a brief account of which has appeared since the 



284 



HOAV CROPS FEED. 



foregoing paragraphs were written. {Jahreshericht il. 
Ag. Chem., 18G5, 29.) 

Bretschneider's experiments were made for the jiurpose 
of estimating how much ammonia, nitric acid, and nitro- 
gen, exist or are formed in the soil, either fallow or occu- 
pied with various crops during the period of growth. 
For this j^urpose he measured oiF in the field four plots of 
ground, each one square rod (Prussian) in area, and sepa- 
rated from the others by paths a yard wide. The soil of 
one plot was dug out to the depth of 12 inches, sifted, 
and after a board frame 12 inches deep had been fitted to 
the sides of the excavation, the sifted earth was filled in 
again. This and another — not sifted — jDlot were planted 
to sugar beets, another was sown to vetches, and the 
fourth to oats. 

At the end of April, six accurate and concordant anal- 
yses were made of the soil. Afterwards, at five different 
periods, a cubic foot of soil was taken from each plot, and 
from the spaces between that bore no vegetation, for de- 
termining the amounts of nitric acid, ammonia, and total 
nitrogen. The results of this analytical work are given 
in the following Tables, being calculated in pounds for the 
area of an acre, and to the depth of 12 inches (English 
measures*) : 







TABLE 


I. 








AMOUNT OF AMMONIA. 








Beet plot, 
sifted sou. 


Beet plot. 


Yetch plot. 


Oatplot. T 


\want I 


End of April, 


59 


59 


59 


59 


59 


12th June, 


15 


48 


41 


32 


28 


30th June, 


12 


41 


24 


40 


32 


2M July, 


9 


29 


39 


22 


29 


13th August, 


8 


15 


16 


11 


43 


9th September, 





16 


16 


1 


23 



* It is plain that when the results of analyses made on a small amount of soil 
are calculated upon the 3,500,000 lbs. of soil (more or less) contained in an acre 
to the depth of one foot (see p. 158), the errors of the analyses, which cannot be 
absolutely exact, are enormously multiplied. What allowance ought to be made 
in this case we cannot say, but should suppose that 5 per cent would not be too 
much. On this basis differences of 200-300 lbs. in Table IV should be overlooked. 



AVAILABLE NITROGEN OF THE SOIL. 



285 







TABLE 


II. 








Amount of nitric acid. 








Beet plot, 
sifted SOU. 


Beet lilot. 


Yetchplot. 


Oat plot. 


Vacant plot. 


End of April, 


56 


56 


56 


56 


56 


12th June, 


281 


270 


102 


28 


106 


30th June, 


328 


412 


15 


93 


318 


22d July, 


116 


89 


58 





43 


13th August, 


53 


6 


71 


14 


81 


9th September, 






TABLE 


12 

in. 








TOTAL ASSIMILABLE NITROGEN (OF 


' AMMONIA AND NITRIC . 


acid). 




Beet plot, 
sifted soil. 


Beet plot. 


Yetchplot. 


Oat plot. 


Vacant plot. 


End of April, 


63 


63 


63 


63 


63 


12th June, 


84 


109 


60 


33 


50 


30th June, 


95 


148 


23 


57 


108 


22d July, 


37 


47 


31 


18 


35 


13th August, 


21 


14 


31 


13 


56 


9th September, 





13 


16 


6 


19 






TABLE 


rv^ 




V 




TOTAL 


NITROGEN 


OF THE SOIL. 








Beet plot, 
sifted soil. 


Beet plot. 


Tetch plot. 


Oat plot. 


Vacant plot. 


End of April, 


4G52 


4652 


4652 


4652 


4652 


12th June, 


4801 


5209 


5606 


6140 


4720 


30th June, 


4667 


5744 


5G88 


5514 


4482 


22d July, 


5398 


5485 




4724 


4924 


13th August. 


5467 


6316 


6316 


6266 


4412 


9th September, 


5164 


4656 


6522 


5004 


4294 



From the first Table we gather that the quantity of 
ammonia^ which was considerable in the spring, dimin- 
ished, especially in a porous (sifted) soil until September. 
In the compact earth of the uncultivated path, its diminu- 
tion was less rapid and less complete. The amount of 
nitric acid (nitrates), on the other hand, increased, though 
not alike in any two cases. It attained its maximum in 
the hot weather- of June, and thence fell off until, at the 
close of the exj^eriments, it was completely wanting save 
in a single instance. 

The figures in the second Table do not represent the 
absolute quantities of nitric acid that existed in the soil 



286 HOV/^ CROPS FEED. 

throughout the j)eriod of experiment, but only those 
amounts that remained at the thne of taking the samples. 
What the vegetation took up from the planted plots, what 
was washed out of the surface soil by rains, or otherwise 
removed by chemical change, does not come into the 
reckoning. 

Those j)lots, the surface soil of which was most occupied 
by active roots, would naturally lose the most nitrates by 
the agency of vegetation ; hence, not unlikely, the vetch 
and oat plots contained so little in June. The results up- 
on the beet, and vacant ground plots demonstrate that in 
that month a rapid formation of nitrates took place. It 
is not, perhaps, impossible that nitrification also proceeded 
vigorously in the loose soils in July and August, but was 
not revealed by the analysis, cither because the vegetation 
took it up or heavy rains washed it out from the surface 
soil. In the brief account of these experiments at hand, 
no information is furnished on these points. Since moist- 
ure is essential to nitrification, it is possible that a period 
of dry weather coming on shortly before the soil was 
analyzed in July, August, and September, had an influence 
on the results. It is certainly remarkable that with the ex- 
ception of the vetch plot, the soil was destitute of nitrates 
on the 9th of September. This plot, at that time, was 
thickly covered with fallen leaves. 

We observe further that the nature of the crops influ- 
enced the accumulation of nitrates, whether simply be- 
cause of the diflferent amount of absorbent rootlets pro- 
duced by them and unequally developed at the given 
period, or for other reasons, we cannot decide.* 

From the third Table may be gathered some idea of the 
total quantity of nitrogen that was present in the soil in 



* It is remarkable that the large-lcavecT beet plant had a great surplus of ni- 
trates, while the oat plot was comparatively deficient in them. Has this fact any 
connection with what has been stated (p. 84) regarding the unequal power of 
plants to provide themselves with nitrogenous food ? 



AVAILABLE NITROGEN OF THE SOIL. 287 

a form available to crops. Assuming that ammonia and 
nitric acid chiefly, if not exclusively, supply vegetation 
with nitrogen, it is seen that the greatest quantity of 
available nitrogen ascertained to be present at any time in 
the soil was 148 lbs. per acre, taken to the depth of one 
foot. This, as regards nitrogen, corresponds to the follow- 
ing dressings: — 

lbs. per acre. 
Saltpeter (nitrate of potash) - - 10G8 

Chili saltpeter (nitrate of soda) - 898 

Sulphate of ammonia - - - - 909 

Peruvian guano (14 per cent of nitrogen) 1057 
The experience of British farmers, among whom all 
the substances above mentioned have been employed, 
being that 2 to 3 cwt. of any one of them make a large, 
and 5 cwt. a very large, application per acre, it is plain 
that in the surface soil of Bretschneider's trials there was 
formed during the groicing season a large manuring of 
nitrates in addition to what was actually consum,ed hy the 
crops. 

The assimilable nitrogen increased in the beet plots up 
to the 30th of June, thence rapidly diminished as it did 
in the soil of the paths. In the oat and vetch plots the 
soil contained, at none of the times of analysis, so much 
assimilable nitrogen as at the beginning of the experi- 
ments. In September, all the plots were much poorer in 
available nitrogen than in the spring. 

Table IV confirms what Boussingault has taught as to 
the vast stores of nitrogen which may exist in the soil. 
The amount here is more than two tons per acre. We ob- 
serve further that in none of the cidtivated plots did this 
amount at any time fall below this figure ; on the other 
hand, in most cases it was considerably increased during the 
period of experiment. In the uncultivated plot, perhaps, 
the total nitrogen fell oif somewhat. This difference may 
have been due to the root fibrils that, in spite of the ut- 



288 



HOW CROPS FEED. 



most care, unavoidably remain in a soil from which grow- 
ing vegetation is removed. The regular and great increase 
of total nitrogen in the vetch plot was certainly due in 
part to the abundance of leaves that fell from the 
plants, and covered the surface of the soil. But this ni- 
trogen, as well as that of the standing crops, must have 
come from the atmosphere, since the soil exhibited no 
diminution in its content of this element. 

We have here confirmation of the view that ammonia^ 
as naturally supplied^ is of very trifling importance to 
vegetation, and that, consequently, nitrates are the chief 
natural means of providing nitrogen for crops. The fact 
that atmospheric nitrogen becomes a part of the soil and 
enters speedily into organic and inert combinations, also 
appears to be sustained by these researches. 

Quantity ©f Nitro^ea needful for Maximum Grain 
Crops. — Hellriegel has made experiments on the effects 
of various quantities of nitrogen (in the form of nitrates) 
on the yield of cereals. The plants grew in an artificial 
soil consisting of pure quartz sand, with an admixture of 
ash-ingredients in such proportions as trial had demon- 
strated to be approimate. All the conditions of the ex- 
periments were made as nearly alike as possible, except as 
regards the amount of nitrogen, which, in a series of eight 
trials, ranged from nothing to 84 parts per 1,000,000 of soil. 

The subjoined Table contains his results. 

EFFECTS OF VARIOUS PROPORTIONS OF ASSDIILABLE NITROGEN 
IN THE SOIL. 



Nitroqen in 






Yield of Grain, in lbs. 






1,000,000 
lbs. of soil. 












Wheat. 


Bye. 


Oats. 




Found 


Calculated 


Found 


Calculated 


Found 


Calculated 





0.002 




0.218 




0.330 






Increase 


~ 


Increase 




Increase 




7 


0.553 


0.926 


0.832 


0.966 


0.929 


1.168 


14 


1.708 


1.851 


1.944 


1.933 


2.605 


2.336 


21 


2.767 


2.777 


2.669 


2.899 


3.845 


3.503 


28 


3.763 


3.703 


4.172 


3.800 


6.211 


4.671 


42 


6.065 


5.554 


5.102 


5.798 


7.030 


7.007 


5G 


7.198 


7.406 


7.163 


7.732 


9.052 


9.342 


84 


9.257 


9.257 


8.698 


8.698 


9.342 


9.342 



DECAY OF NITROGENOUS BODIES. 289 

From numerous other experiments, not published at 
this writing, Hellriegel believes himself justified in assum- 
ing that the highest yield thus observed, with 84 lbs. of 
nitrogen in 1,000,000 of soil, might have been got with 
70 lbs. of nitrogen in case of wheat, with 63 lbs. in case 
of rye, and with 56 lbs. in case of oats. On this assump- 
tion he has calculated the yield of each of these crops, 
and the figures obtained (see Table) present on the whole 
a remarkable coincidence with those directly observed. 

§ -r. 

DECAY OF NITROGENOUS BODIES. 

We have incidentally noticed some of the products of 
the decay of nitrogenous bodies, viz., those which remain 
in the soil. We may now, with advantage, review the 
subject connectedly, and make our account of this process 
more complete. 

It will be needful in the first place to give some ex- 
planations concerning the nature of the familiar trans- 
formations to which animal and vegetable matters are 
subject. 

By the word decay, as popularly employed, is under- 
stood a series of chemical changes which are very difier- 
ent in their manifestations and results, according to the 
circumstances under which they take place or the kinds 
of matter they attack. Under one set of conditions we 
have slow decay, or, as Liebig has fitly designated it, 
even ausis y* under others fermentation ; and under still 
others putrefaction, 

EremecausiS* is a slow oxidation, and requires the 
constant presence of an excess of free oxygen. It pro- 
ceeds upon vegetable matters which are comparatively 



•From the Greek, signifying slmo combustion. 

13 



290 HOW CEOPS FEED. 

difficult of alteration, such as stems and leaves, consist- 
ing chiefly of cellulose, with but little albuminoids, and 
both in insoluble forms. 

What is said in a former paragraph on the " Decay of 
Vegetation," p. 137, applies in general to eremecausis. 

Fermentation is a term commonly applied to any 
seemingly spontaneous change taking place with vegeta- 
ble or animal matters, wherein their sensible qualities 
sufier alteration, and heat becomes perceptible, or gas is 
rapidly evolved. Chemically speaking, fermentation is 
the breaking up of an organic body by chemical decom- 
position, which may go on in absence of oxygen, and is 
excited by a substance or an organism called a ferment. 

There are a variety of fermentations, viz., the vinous^ acetic, lactic, etc. 
In vinous fermentation, the yeast-fungus, Tot-vula ce}-evisice, vegetates 
in an impure solution of sugar, and causes the latter to breaic iip into 
alcohol and carbonic acid Avith small quautities of other products. la 
the acetic fermentation, the vinegar-plant, Ilycoderma vini, is believed 
to facilitate the conversion of alcohol into acetic acid, but this change 
is also accomplished by jplatinum sponge, which acts as a ferment. In 
the lactic fermentation, a fungus, Fcnicilium glaucum, is thought to de- 
termine the conversion of sugar into lactic acid, as in the souring of milk. 

The transformation of starch into sugar has been termed the saccha- 
rous fermentation, diastase being the ferment. 

Putrefaction, or putrid fermentation, is a rapid internal 
change which proceeds in comparative absence of oxygen. 
It most readily attacks animal matters which are rich in 
albuminoids and other nitrogenous and sulphurized prin- 
ciples, as flesh, blood, and urine, or the highly nitrogenous 
parts of plants, as seeds, when they are fully saturated 
with water. Putrefying matters commonly disengage 
stinking gases. According to Pasteur putrefaction is oc- 
casioned by the growth of animalcules ( Vibrios). 
I Fermentation is usually and putrefaction is always a 
reducing (deoxidizing) process, for either the ferment it- 
self or the decomposing substances, or some of the prod- 
ucts of decomposition, are highly prone to oxidation, and 



DECAY OF NITROGENOUS BODIES. 391 

in absence of free oxygen may remove this element from 
reducible bodies (Traube, Fermentwirkungen^ pp. 63-78). 

In a mixture of cellulose, sugar, and albuminoids, ere- 
mecausis, fermentation, and putrefaction, may all proceed 
simultaneously. 

When the albuminoids decay in the soil associated with 
carbohydrates and humus, the final results of their altera- 
tion may be summed up as follows : 

1. Carbon unites mainly with oxygen, forming carbonic 
acid gas, which escapes into the atmosphere. With im- 
perfect supplies of oxygen, as when submerged in water, 
carbonic oxide (CO) and marsh gas (CHJ are formed. A 
portion of carbon remains as humus. 

2. Hydrogen^ for the most part, combines with oxygen, 
yielding water. In deficiency of oxygen, some hydrogen 
escapes as a carbon compound (marsh-gas), or in the free 
state. If humus remains, hydrogen is one of its con- 
stituents. 

3. a. Nitrogen always unites to a large extent with 
hydrogen, giving ammonia, which escapes as gaseous car- 
bonate in considerable quantity, unless from presence of 
carbohydrates much humus is formed, in which case it 
may be nearly or entirely retained by the latter. Lawes, 
Gilbert, and Pugh, {Phil Trans. 1861, II., p. 501) made 
observations on the decay of wheat, barley, and bean 
seeds, either entire or in form of meal, mixed with a large 
quantity of soil or powdered jDumice, and exposed in vari- 
ous conditions of moisture to a current of air for six 
months. They found in nine experiments that from 11 to 
58^*1^ of the nitrogen was converted into ammonia, al- 
though but a trifling proportion of this (on the average 
but 0.4"! J escaped in the gaseous form. 

h. In presence of excess of oxygen, a portion of nitro- 
gen usually escapes in the free state. Reiset proved the 
escape of free nitrogen from fermenting dung. Boussin- 



292 HOW CROPS FEED. 

gault, in his investigations on the assimilability of free 
nitrogen, found in various vegetation-experiments, in 
which crushed seeds were used as fertilizers, that nitrogen 
was lost by assuming some gaseows form. This loss prob- 
ably took place to some slight extent as ammonia, but 
chiefly as free nitrogen. Lawes, Gilbert, and Pugh, found 
in thirteen out of fifteen trials, including the experiments 
just referred to, that a loss of free nitrogen took place, 
ranging from 2 to 40 per cent of the total quantity con- 
tained originally in the vegetable matters submitted to 
decomposition. In six experiments the loss was 12 to 13 
per cent. In the two cases where no loss of nitrogen oc- 
curred, nothing in the circumstances of decay was discov- 
erable to which such exceptional results could be at- 
tributed. Other experiments {Phil. Trans. 1861, II., p. 
509) demonstrated that in absence of oxygen no nitrogen 
was evolved in the free state. 

c. Nitric acid is not formed from the nitrogen of or- 
ganic bodies in rapid or putrefactive decay, but only in 
slow oxidation or eremecausis of humified matters. 
Pelouze found no nitrates in the liquor of dung heaps. 
Lawes, Gilbert, and Pugh, {loc. c/^.)* found no nitric acid 
when the seed-grains decayed in ordinary air, nor was it 
produced when ozonized air was passed over moist bean- 
meal, either alone or mixed with burned soil or with 
slaked lime, the experiments lasting several months. It 
thus appears that the carbon and hydrogen of organic 
matters have such an affinity for oxygen as to prevent the 
nitrogen from acquiring it in the quicker stages of decay. 
More than this, as Pelouze has shown ( Comptes Bendus^ 
XLIV., p. 118), putrefying matters rob nitric acid of its 
oxygen and convert it into ammonia. We have already 
remarked that putrefaction and fermentation are reducing 
processes, and until they have run their course and the 
organic matters have passed into the comparatively stable 
forms of humus, their nitrogen appears to be incapable of 



THE NITROGENOUS PEINCIPLES OF URINE. 293 

oxidation. So soon as compounds of carbon and hydrogen 
are formed, which imite but slowly with free oxygen, so 
that the latter easily maintains itself in excess, then and 
not before, the nitrogen begins to combine with oxygen. 
4. Finally, the sulphur of the albuminoids may be at 
first partially dissipated as sulphuretted hydrogen gas, 
while in the slower stages of decay, it is oxidized to sul- 
phuric acid, which remains as sulphates in the soil. 



THE NITROGENOUS PRINCIPLES OF URINE. 

The question " How Crops Feed " is not fully answered 
as regards the element Nitrogen, without a consideration 
of certain substances — ingredients of urine — which may 
become incorporated with the soil in the use of animal 
manures. 

Professor Way, in his investigation on the " Power of 
Soils to Absorb Manure," describes the following remark- 
able experiment : " Three quantities of fresh urine, of 
2,000 grains each, were measured out into similar glasses. 
With one portion its own weight of sand was mixed ; 
with another, its own weight of white clay ; the tbird 
being left without admixture of any kind. When smelt 
immediately after mixture, the sand appeared to have 
had no effect, Avhilst the clay mixture had entirely lost 
thfe smell of urine. The three glasses were covered light- 
ly with j^aper and put in a warm place, being examined 
from time to time. In a few hours it was found that the 
urine containing sand had become slightly putrid ; then 
followed the natural urine ; but the quantity with which 
clay had been mixed did not hecome putrid at aU^ and 
at the end of seven or eight weeks it had only the pecu- 
liar smell of fresh urine, without the slightest putridity. 
The surface of the clay, however, became afterwards cov- 



294 HOW CROPS PEED. 

ered with a luxuriant growth of conferva?, which did not 
happen in the other glasses." {Jour, Hoy. Ag. Soc. of 
Eng., XL, S66.) 

Professor Way likewise found that filtering urine 
through clay or simply shaking the two together, allow- 
ing the liquid to clear itself, and pouring it off, sufficed to 
prevent putrefaction, and keep the urine as if fresh for a 
month or more. Cloez found, as stated on p. 264, that in 
a mixture of moistened pumice-stone, carbonate of lime, 
and urea (the nitrogenous principle of urine), no nitrates 
"were formed during eight months' exposure to a slow 
current of air. 

These facts make it necessary to consider in what state 
the nitrogen of urine is absorbed and assimilated by 
vegetation. 

Urine contains a number of compounds rich in nitro- 
gen, being derived from the waste of the food and tissues 
of the animal, which require a brief notice. 

Urea (CO N^HJ* may be obtained from the urine of 
man as a white crystalline mass or in distinct transparent 
rhombic crystals, which remain indefinitely unaltered iu 
dry air, and have a cooling, bitterish taste like saltpeter. 
It is a weak base, and chemists have prepared its nitrate, 
oxalate, phosphate, etc. 

Urea constitutes 2 to 3 per cent of healthy human 
urine, and a full-grown and robust man excretes of it 
about 40 grams, or V\^07,. av. daily. 

When urine is left to itself, it shortly emits a putrid 
odor ; after a few days or hours the urea it contained en- 
tirely disappears, and the liquid smells powerfully of am- 
monia. Urea, when in contact with the animal matters 



* Carbon 20.00 

Hydrogen 6.67 

Nitrogen 46.67 

Oxygep 26.66 

100.00 



THE NITROGENOUS PRINCIPLES OF URINE. 295. 

of urine, suffers decomposition, and its elements, combin- 
ing with the elements of water, are completely transformed 
into carbonate of ammonia. 

Urea. Water. Carbonate of Ammonia. 

CO J^M^ + 2H,0 = 2(NH3), H,0,CO,. 

As we have learned from Way's experiments, clay is 
able to remove from urine the *' ferment " which occasions 
its putrefaction. 

Urea is abundant in the urine of all carnivorous and 
herbivorous mammals, and exists in small quantity in the 
urine of carnivorous birds, but has not been detected in 
that of herbivorous birds. 

Uric acid (C^H^N^Og)* is always present in healthy 
human urine, but in very minute quantity. It is the chief 
solid ingredient of the urine of birds and reptiles. Here 
it exists mainly as urate of ammonia.** The urine of 
birds and serpents is expelled from the intestine as a w^hite, 
thickish liquid, which dries to a chalk-like mass. From 
this, uric acid may be obtained in the form of a white 
powder, which, when magnified, is seen to consist of mi- 
nute crystals. By powerful oxidizing agents uric acid is 
converted into oxalate and carbonate of ammonia, and 
urea. Peruvian guano, when of good quality, contains 
some 10 per cent of urate of ammonia. 

Hippuric acid (CgH^IsrOJt is commonly abundant in 
the urine of the ox, horse, and other herbivorous animals. 
By boiling dowm fresh urine of the pastured or hay-fed 
cow to ^ Ig its bulk, and adding hydrochloric acid, hippuric 
acid crystallizes out on cooling in four-sided prisms, of- 
ten two or three inches in length. 



♦ Carbon 35.72 ♦♦Carbon 32.43 t Carbon 60.74 

Hydrogen 2.38 Hydrogen 3.TS Hydrogen 4.96 

Nitrogen 33.33 Nitrogen 37.84 Nitrogen 7.88 

Oxygen 28.57 Oxygen 25.95 Oxygen 26.48 

100.00 100.00 100.00 



296 



HOW CROPS FEED. 



Glycocoll or Glycine* is a sweet substance that re- 
sults from the decomposition of hippuric acid under the 
influence of various agents. It is also a product of the 
action of acids on gelatine and horn. 

Guanine (C^H^N^O) f occurs to the extent of about 
^ I, per cent in Peruvian guano, and is an ingredient of 
the liver and pancreas of animals, whence it passes into 
the excrement in case of birds and spiders. By oxidation 
it yields among other products urea and oxalic acid. 

Kreatin (0,113^30^ I is an organic base existing in 
very minute quantity in the flesh of animals, and occa- 
sionally found in urine. 

Cameron was the first, in 1857, to investigate the assimi- 
lability of urinary products by vegetation. His experi- 
ments (Cheinistry of Agriculture, pp. 139-144) were 
made with barley, which was sown in an artificial soil, 
destitute of nitrogen. Of four pots one remained without 
a supply of nitrogen, another was manured with sulphate 
of ammonia, and two received a solution of urea. The 
pot without nitrogen gave plants 8 inches high, but these 
developed no seeds. The pot with sulphate of ammonia 
gave plants 22 inches high, and 300 seeds. Those with 
urea gave respectively stalks of 26 and 29 inches height, 
and 252 and 270 seeds. The soil in neither case contained 
ammonia, the usual decomposition-product of urea. Dr. 
Cameron justly concluded that urea enters plants un- 
changed, is assimilated by them, and equals ammonia-salts 
as a means of supplying nitrogen to vegetation. 

The next studies in this direction were made by the au- 
thor in 1861 {Am, Jour. Science, XLL, 27). Experiments 
were conducted with uric acid, hippuric acid, and guanine. 

* Carbon 39.73 + Carbon 32.00 $ Carbon.. 36.64 

Hydrogen 3.31 Hydrogen 6.67 Hydrogen 6.87 

Nitrogen 46.36 Nitrogen 18.67 Nitrogen 32.06 

Oxygen lO.eO Oxygen 42.66 Oxygen 24.43 

100.00 100.00 looioo 



THE nttroge:n^ous principles op urine. 297 

"Washed and ignited flower-pots were employed, to con- 
tain, for each trial, a soil consisting of 700 grms. of 
ignited and washed granitic sand, mixed with 0.25 grm. 
sulphate of lime, 2 grms. ashes of hay, prepared in a muffle, 
and 2.75 grms. bone-ashes. This soil w^as placed upon 
100 grms. of clean gravel to serve as drainage. 

In each of four pots containing the above soil was de- 
posited, July 6th, a weighed kernel of maize. The pots 
were watered with equal quantities of distilled water con- 
taining a scarcely appreciable trace of ammonia. The 
seeds germinated in a healthy manner, the plants devel- 
oped slowly and alike imtil July 28th, when the addition 
of nitrogenous matters w^as begun. 

To No. 1, no solid addition was made. 

To No. 2 was added, July 28th, 0.420 grm. uric acid. 

To No. 3 was added 1.790 grm. hippuric acid, at four 
different times, viz: July 28,0.358 grm., Aug. 26th, 0.358 
grm., Sept. 16th, 0.716 grm., Oct. 3d, 0.358 grm. 

To No. 4 was added 0.4110 grm. hydrochlorate of gua- 
nme, viz: July 28th, 0.0822 grm., Aug. 26th, 0.0822 
grm., Sept. 16th, 0.1644 grm., Oct. 3d, 0.0822 grm. 

The nitrogenous additions contained in each case, 0.140 
grm. of nitrogen, and were strewn, as fine powder, over 
the surface of the soil. 

The plants continued to grow or to remain healthy (the 
lower leaves withering more or less) until they were re- 
moved from the soil, Nov. 8th. 

The plants exhibited striking differences in their devel- 
opment. No. 1 (no added nitrogen) produced in all seven 
slender leaves, and attained a height of 7 inches. At the 
close of the experiment, only the two newest leaves were 
perfectly fresh ; the next was withered and dead through- 
out one-third of its length. The newer portions of this 
plant grew chiefly at the expense of the older parts. No 
sign of floral organs appeared. 
13* 



298 HOW CROPS FEED. 

No. 2, fed with uric acid, was the best developed plant 
of the series. At the conclusion of the experiment, it 
bore ten vigorous leaves, six of which were fresh, and two 
but partly withered. It Avas 14 inches high, and carried 
two rudimentary ears (pistillate flowers), from the upper 
one of which hung tassels 6 inches long. 

No. 3, supplied with hippuric acid, bore eight leaves, 
four of which were withered, and two rudimentary ears,j 
one of which tasseled. Height, 12 inches. 

ISTo. 4, with hydrochlorate of guanine, had six leaves, 
one withered, and two ears, one of which was tasseled. 
Height, 12 inches. The weight of the crops (dried at 
212° F.), exclusive of the fine rootlets that could not be 
removed from the soil, was ascertained, with the subjoined 

results. 

1 2 3 4 

Without Hippuric 

Nitrogen. Uric Acid. Acid. Guanine. 

Weight of dried crop, 0.1925 grm. 1.9470 grm. 1.0149 grm. 0.9820 grm. 
" " seed, 0.1644 *' .1725 " 0.1752 *' 0.1698 *' 



gam, 



0.0391 " 1.7745 " 0.8397 " 0.8123 



We thus have proof that all the substances employed 
contributed nitrogen to the growing plant. This is con- 
clusively shown by the fact that the development of pis- 
tillate organs, which are especially rich in nitrogen, 
occurred in the three plants fed wdth nitrogenous com- 
pounds, but was totally wanting in the other. The rela- 
tion of matter, new-organized by growth, to that derived 
from the seed, is strikingly seen from a comparison of the 
ratios of the weight of the seed to the increase of organ- 
ized matter, the former being taken as unity. 

The ratio is approximatively 
for No. 1, 



1, 


1 


: 0.2 


2, 


1 


: 10.2 


3, 


1 


: 4.8 


4, 


1 


: 4.8 



THE NITEOGEXOUS PRINCIPLES OF URINE. 299 

The relative gain by growth, that o"^ No. 1 assumed as 
unity, is for No. 1, — 1 

« " 2, — 61 
« u 3^ _ 29 

" " 4, — 28 
The crops were small, principally because the supply 
ofcinitrogen was very limited. 

These experiments demonstrate that the substances 
added, in every case, aided growth by supplying nitro- 
gen. They do not, indeed, prove that the organic fertil- 
izers entered as such into the crop without decomposition, 
but if urea escapes decomposition in a soil, as Cameron 
and Cloez have shown is true, it is not to be anticipated 
that the bodies employed in these trials should suffer al- 
teration to ammonia-salts or nitrates. 

Hampe afterAvards experimented with urea and uric 
acid by the method of Water-Culture ( Vs. St., YH., 308 ; 
YITL, 225 ; IX., 49 ; and X., 175). He succeeded in pro- 
ducing, by help of urea, maize plants as large as those 
growing in garden soil, and fully confirmed Cameron's 
conclusion regarding the assimil ability of this substance. 
Hampe demonstrated that urea entered as such into the 
plant. In fact, he separated it, in the pure state, from 
the stems and leaves of the maize which had been pro- 
duced with its aid. 

Hampe's experiments with uric acid in solution showed 
that this body supplied nitrogen without first assuming 
the fonn of ammonia-salts, but it suffered partially if not 
entirely a decomposition, the nature of which was not 
determined. Uric acid itself could not be found in the 
crop. 

Hampe's results with hippuric acid were to the effect 
that this substance furnishes nitrogen without reversion 
to ammonia, but is resolved into other bodies, probably 
benzoic acid and glycocoll, which are formed when hip- 



300 HOW CROPS FEED. 

puric acid is subjected to the action of strong acids or 
ferments. 

Hampe, therefore, experimented with glycocoll, and 
from his trials formed the opinion that this body is di- 
rectly nutritive. In fact, he obtained with it a crop equal 
to that yielded by ammonia-salts. 

Knoj), who made, in 1857, an unsuccessful experiment 
with hippuric acid, found, in 1866, that glycocoll is as- 
similated {Chem. CentralUatt, 1866, p. 774). 

In 1868, "Wagner experimented anew with hippuric 
acid and glycocoll. His results confirm those of Hampe. 
Wagner, however, deems it probable that hippuric acid 
enters the plant as such, and is decomposed within it into 
benzoic acid and glycocoll ( T^. St.^ XL, p. 294). 

"Wagner found, also, that kreatin is assimilated by 
vegetation. 

The grand result of these researches is, that the nitrog- 
enous (amide-like) acids and bases which are thrown off 
in the urinary excretions of animals need not revert, by 
decay or putrefaction, to inorganic bodies (ammonia or 
nitric acid), in order to nourish vegetation, but are either 
immediately, or after undergoing a slight and easy altera- 
tion, taken up and assimilated by growing plants. 

As a practical result, these facts show that it is not 
necessary that urine should be fermented before using it 
as a fertilizer. 

COMPARATIVE NUTRITIVE VALUE OF AMMONIA-SALTS AND 
NITRATES. 

The evidence that both ammonia and nitric acid are ca- 
pable of supplying nitrogen to plants has been set forth. 
It Ijas been shown further that nitric acid alone can per- 
fectly 'satisfy the wants of vegetation as regards the ele- 
ment nitrogen. In respect to ammonia, the case has not 



VALUE OF AMMONIA AND NITEIC ACID. 



301 



been similarly made out. We have learned that ammonia 
occurs, naturally, in too small jDroportion, either in the 
atmosphere or the soil, to supply much nitrogen to crops. 
In exceptional cases, however, as in the leaf-mold of Rio 
Cupari, exammed by Boussingault, p. 276, as well as in 
lands manured with fermenting dung, or with sulphate or 
muriate of ammonia, this substance acquires importance 
from its quantity. 

On the assumption that it is the nitrogen of these sub- 
stances, and not their hydrogen or oxygen, which is of 
value to the plant, we should anticipate that 17 parts of 
ammonia would equal 54 parts of nitric acid in nutritive 
effect, since each of these quantities represents the same 
amount (14 parts) of nitrogen. The ease with which 
ammonia and nitric acid are mutually transformed favors 
this view, but the facts of experience in the actual feed- 
ing of vegetation do not, as yet, admit of its acceptance. 

In earlier vegetation-experiments, wherein the nitro- 
genous part of an artificial soil (without humus or clay) 
consisted of ammonia-salts, it v/as found that these were 
decidedly inferior to nitrates in their producing power. 
This was observed by Ville in trials made with wheat 
planted in calcined sand, to which was added a given 
quantity of nitrogen in the several forms of nitrate of 
potash, sal-ammoniac (chloride of ammonium), nitrate of 
ammonia, and phosphate of ammonia. 

Yille's results are detailed in the following table. The 
quantity of nitrogen added was 0.110 grm. in each case. 



Source of Nitrogen. 


straw and 
Roots. 


Grain. 


Average 
crop. 


Nitrogen 

in average 

crop. 


Nitrate of Potash ■< 


I. 20.70 
IL 19.22 

X. 15.10 
II. 17.34 

I. 12.20 
II. 14.87 

I. 12.96 
II. 15.82 


6.20 


i .26 71 


0.221 


Sal-ammoiiiac i 


7.30 ) 

|:9|i... 18.83 

i:l[...18.33 

l-l]\ ...18.40 


0.142 




0.133 


Phosphate of ammonia i 


0.133 




4.34 







302 HOW CROPS FEED. 

It is seen that the ammonia-salts gave about one-fourth 
less croj) than the nitrate of potash. The potash doubt- 
less contributed somewhat to this difference. 

The author began some experiments on this point in 
1861, which turned out unsatisfactorily on account of the 
want of light in the apartment. In a number of these, 
buckwheat, sown in a weathered feldspathic sand, was ma- 
nured with equal quantities of nitrogen, potash, lime, 
phosphoric acid, sulphuric acid, and chlorine, the nitrogen 
being presented in one instance in form of nitrate of jDotash, 
in the others as an ammonia-salt — sulphate, muriate, phos- 
phate, or oxalate. 

Although the plants failed to mature, from the cause 
above mentioned, the experiments plainly indicated the 
inferiority of ammonia as compared with nitric acid. 

Explanations of this fact are not difficult to suggest. 
The most reasonable one is, j^erhaps, to be found in the 
circumstance that clayey matters (which existed in the 
soil under consideration) " fix " ammonia, i. e., convert it 
into a comparatively insoluble compound, so that the 
plant may not be able to apj^ropriate it all. 

On the other hand, Hellriegel [Ann. d. Landw.^ VII., 
53, u. YIII, 119) got a better yield of clover in artificial 
soil with sulphate of ammonia and phosphate of ammonia 
than with nitrate of ammonia or nitrate of soda, the quan- 
tity of nitrogen being in all cases the same. 
* As Sachs and Knop developed the method of Water- 
Culture, it was found by the latter that ammonia-salts did 
not effectively replace nitrates. The same conclusion was 
arrived at by Stohmann, in 1861 and 1863 [Ilenneberg' s 
Journ.^ 1862, 1, and 1864, 65), and by Rautenberg and 
Kuhn,in 1863 {Henneherg' s Journ., 1864, 107), who ex- 
perimented with sal-ammoniac, as well as by Birner and 
Lucanus, in 1864 {Vs. St., YIIL, 152), who employed 
sulphate and phosphate of ammonia. 

The cause of failure lay doubtless in the foct, first noticed 



VALUE OF AMilOXIA AND NITRIC ACID. 303 

by Ktihii, that so soon as ammonia was taken up by the 
plant, the acid with which it was combined, becoming free, 
acted as a poison. 

In 1866, Hampe ( Vs. jSt., IX., 165), using phosphate 
of ammonia as the single source of nitrogen, and taking 
care to keep the solution but faintly acid, obtained a 
maize-plant which had a dry weight of 18 grams, includ- 
ing 36 perfect seeds ; no nitrates were formed in the 
solution. 

The same summer Kiihn ( Vs. St., IX., 167) produced 
two small maize-plants, one with phosphate, the other 
with sulphate of ammonia as the source of nitrogen, but 
his experiments were interrupted by excessive heat in the 
glass-house. 

In 1866, Beyer {Vs. St., IX., 480) also made trials on 
the growth of the oat-plant in a solution containing bi- 
carbonate of ammonia. The plants vegetated, though 
poorly, and several blossomed and even produced a few 
seeds. Quite at the close of the experiments the plants 
suddenly began to grow, with formation of new shoots. 
Examination of the liquid showed that the ammonia had 
been almost completely converted into nitric acid, and the 
increased growth was obviously connected with this nitrifi- 
cation. 

In 1867, Hampe ( Vs. St., X., 176) made new experi- 
ments with ammonia-salts, and obtained one maize-plant 
2^1 2 ft. high, bearing 40 handsome seeds, and weighing, 
dry, 25^ |„ grams. In these trials the seedlings, at the 
time of unfolding the sixth or seventh leaf, after consum- 
ing the nutriment of the seeds, manifested remarkable 
symptoms of disturbed nutrition, growth being sup- 
pressed, and the foliage becoming yellow. After a week 
or two the plants recovered their green color, began to 
grow again, and preserved a healthy appearance until 
mature. Experiment demonstrated that this diseased 
state was not afiected by the concentration of the nour- 



304 HOW CROPS FEED. 

isliing solution, by the amount of free acid or of iron 
present, nor by the illumination. Hampe observed that 
from these trials it seemed that the plants, while young, 
were unable to assimilate ammonia or did so with diffi- 
cidty, hut acquired the power with a certain age. 

In 1868, Wagner ( Vs. St., XL, 288) obtained exactly 
the same results as Hampe. He found also that a maize- 
seedling, allowed to vegetate for two weeks in an artificial 
soil, and then placed in the nutritive solution, with phos- 
phate of ammonia as a source of nitrogen, grew nor- 
mally, without any symptoms of disease. AYagner ob- 
tained one plant weighing, dry, 26^ 1^ grams, and carrying 
48 ripe seeds. In experiments with carbonate of ammonia, 
"Wagner obtained the same negative result as Beyer liad 
experienced in 1866. 

Beyer reports ( Vs. St., XL, 267) that his attempts to 
nourish the oat-plant in solutions containing ammonia- 
salts as the single source of nitrogen invariably failed, 
although repeated through three summers, and varied in 
several ways. Even with solutions identical to those in 
which maize gre\v successfully for Hampe, the oat seed- 
lings refused to increase notably in weight, every precau- 
tion that could be thought of being taken to provide 
fxvorable conditions. It is not impossible that all these 
failures to supply plants with nitrogen by the use of am- 
monia-salts depend not upon the incapacity of vegetation 
to assimilate ammonia, but upon other conditions, unfa- 
vorable to growth, which are inseparable from the meth- 
ods of experiment. A plant growing in a solution or in 
pure quartz sand is in abnormal circumstances, in so far 
that neither of these media can exert absorbent power 
sufficient to remove from solution and make innocuous any 
substance which may be set free by the selective agency 
of the plant. 

Furtlier investigations must be awaited before this 
point can be definitely settled. It is, however, a matter 



CONSTITUTION OF TlIK SOIL. 305 

of little practical importance, since ammonia is so sparse- 
ly supplied by nature, and the ammonia of fertilizers is 
almost invariably subjected to the conditions of speedy 
nitrification. 



CHAPTER VI. 

THE SOIL AS A SOURCE OF FOOD TO CROPS.— INGRE- 
DIENTS AVIIOSE ELEMENTS ARE DERIVED FROM 
ROCKS. 

§1. 

GENERAL VIEW OF THE CONSTITUTION OF THE SOIL AS 
RELATED TO VEGETABLE NUTRITION. 

Inert, Active, and Reserve Matters. — In all cases the 
soil consists in great part of matters that are of no direct 
or present use in feeding the plant. The chemical nature 
of this inert portion may vary greatly without correspond- 
ingly influencing the fertility of the soil. Sand, either 
quartzose, calcareous, micaceous, feldspathic, hornblendic, 
or augitic ; clay in its many varieties ; chalk, ocher (oxide 
of iron), humus ; in short, any porous or granular material 
that is insoluble and little alterable by weather, may con- 
stitute the mass of the soil. The physical and mechanical 
characters of the soil are chiefly influenced by those ingre- 
dients which preponderate in quantity. Hence Yille has. 
quite appropriately designated them the "mechanical 
agents of the soiL" They afiect fertility principally as 
they relate the plant to moisture and to temperature. 
They also have an influence on crops by gradually assum- 
ing more active forms, and yielding nourishment as the 
result of chemical changes. In general, it is probable 



896 HOW CROPS FEED. 

that 99 per cent and more of the soil, exclusive of water, 
does not in the slightest degree contribute directly to the 
support of the present vegetation of our ordinary field 
products. 

The hay crop is one that takes up and removes from 
the soil the largest quantity of mineral matters (ash- 
ingredients), but even a cutting of 2|- tons of hay car- 
ries off no more than 400 lbs. per acre. From the 
data given on page 158, we may assume the weight of 
the soil upon an acre, taken to the depth of one foot, 
to be 4,000,000 lbs. The ash-ingredients of a heavy 
hay crop amount therefore to but one ten-thousandth of 
the soil, admitting the crop to be fed exclusively by the 
12 inches next the surface. Accordingly no less than 100 
full crops of hay would require to be taken oif to consume 
one per cent of the weight of the soil to this depth. "We 
confine our calculation to the ash-ingredients because we 
have learned that the atmosphere furnishes the main sup- 
ply of the food from which the combustible i^art of the 
crop is organized. Should we spread out over the surface 
of an acre of rock 4,000,000 lbs. of the purest quartz 
sand, and sow the usual amount of seed upon it, maintain- 
ing it in the proper state of moisture, etc., we could not 
produce a crop ; we could not even recover the seed. Such 
a soil would be sterile in the most emphatic sense. But 
should we incorporate with such a soil a few thousand 
lbs. of the mineral ingredients of agricultural plants, to- 
gether with some nitrates in the appropriate combinations 
and proportions, we should bestow fertility ujDon it by this 
addition and be able to realize a crop. Should we add to 
our acre of pure quartz the ashes of a hay crop, 400 lbs., 
and a proper quantity of nitrate of potash, we might also 
realize a good crop, could we but ensure contact of the 
roots of the plants with all the added matters. But in 
this case the soil would be fertile for one crop only, and 
after the removal of the latter it would be as sterile as 



CONSTITUTION OF THE SOIL. 307 

before. We gather, then, that there are three items to be 
regarded in the simplest view of the chemical comjDo- 
sition of the soil, viz., the inert mechanical basis, the 
presently available nutritive ingredients, and the reserve 
matters from which the available ingredients are supplied 
as needed. 

In a previous chapter we have traced the formation of 
the soil from rocks by the conjoint agencies of mechanical 
and chemical disintegration. It is the perpetual operation 
of these agencies, especially those of the chemical kind, 
which serves to maintain fertility. The fragments of rock, 
and the insoluble matters generally that exist in the soil, 
are constantly suffering decomposition, whereby the ele- 
ments that feed vegetation become available. "What, 
therefore, we have designated as the inert basis of the soil, 
is inert for the moment only. From it, by perpetual 
change, is preparing the available food of crops. Various 
attempts have been made to distinguish in fact between 
these three classes or conditions of soil-ingredients ; but 
the distinction is to us one of idea only. We cannot realize 
their separation, nor can we even define their peculiar con- 
ditions. We are ignorant in great degree of the power 
of the roots of plants to imbibe their food ; we are equally 
ignorant of the mode in which the elements of the soil are 
associated and combined ; we have, too, a very imperfect 
knowledge of the chemical transformations and decomposi- 
tions thp.t occur within it. We cannot, therefore, dissect 
the soil and decide what and how much is immediately 
available, and what is not. Furthermore, the soil is chem- 
ically so complex, and its relations to the plant are so com- 
plicated by j^hysical and physiological conditions, that wa 
may, perhaps, never arrive at a clear and unconfused idea 
of the mode by which it nourishes a crop. ^Nevertheless, 
what we have attained of knowledge and insight in this 
direction is full of value and encouragement. 

Deportment of the Soil towards Solrents.— When we 



308 HOW CKOPS PEED. 

put a soil in contact with water, certain matters are dis- 
solved in this liquid. It has been thought that the sub- 
stances taken up by water at any moment are those which 
at that time represent the available plant-food. This no- 
tion was based upon the supposition that the plant cannot 
feed itself at the roots save by matters in solution. Since 
Liebig has brought into prominence the doctrine that roots 
are able to attack and dissolve the insoluble ingredients 
of the soil, this idea is generally regarded as no longer 
tenable. 

Agam, it has been taught that the reserve plant-food of 
the soil is represented by the matters which acids (hydro- 
chloric or nitric acid) are capable of bringing into solu- 
tion. This is true in a certain rough sense only. The 
action of hydrochloric or nitric acid is indeed analogous 
to that of carbonic acid, which is the natural solvent ; but 
between the two there are great differences, independent 
of those of degree. 

Although we have no means of learning with positive 
accuracy Avhat is the condition of the insoluble ingredients 
of the soil as to present or remote availability, the deport- 
ment of the soil towards water and acids is highly in- 
structive, and by its study Ave make some approach to the 
solution of this question. 

Standards of Solubility, — Before proceeding to details, 
some words upon the limits of solubility and upon what 
is meant by soluble in water or in acids will be appropri- 
ate. The terms soluble and insoluble are to a great de- 
gree relative as applied to the ingredients of the soil. 
When it is affirmed that salt is soluble in water, and that 
glass is insoluble in that liquid, the meaning of the state- 
ment is plain ; it is simply that salt is readily recognized 
to be soluble and that glass is not ordinarily perceived to 
dissolve. The statement that glass is insoluble is, however, 
only true when the ordinary standards of solubility arc re- 
ferred to. The glass bottle Avhich may contain water for 



AQUEOUS SOLUTION OF THE SOIL. 309 

years "without perceptibly yielding aught of its mass to the 
liquid, does, nevertheless, slowly dissolve. We may make 
its solubility perceptible by a simple expedient. Pulver- 
ize the bottle to the finest dust, and thus extend the sur- 
face of glass many thousand or million times ; weigh the 
glass-powder accurately, then agitate it for a few minutes 
with water, remove the liquid, dry and weigh the glass 
again. We shall thus find that the glass has lost several 
per cent of its original weight (Pelouze), and by evapo- 
rating the water, it will leave a solid residue equal in 
weight to the loss experienced by the glass. 

AQUEOUS SOLUTION OF THE SOIL. 

The soil and the rocks from which it is formed would 
commonly be spoken of as insoluble in water. They are, 
however, soluble to a slight extent, or rather, we should 
say, they contain soluble matters. 

The quantity that water dissolves from a soil depends 
upon the amount of the liquid and the duration of its 
contact ; it is therefore necessary, in order to estimate 
properly any statements respecting the solubility of the 
soil, to know the method and conditions of the experi- 
ment upon which such statements are based. 

We subjoin the results of various investigations that 
exhibit the general nature and amount of matters soluble 
in water. 

In 1852 Yerdeil and Risler examined 10 soils from the 
grounds of the InstUut Agronomique, at Versailles. In 
each case about 22 lbs. of the fine earth were mixed with 
pure lukewarm water to the consistence of a thin pap, 
and after standing several hours with frequent agitation 
the water was poured off; this process was repeated to 
the third time. The clear, faintly yellow solutions thus 
obtained were evaporated to dryness, and the residues 
were analyzed with results as follows, per cent : 



310 



HOW CKOPS FEED. 





=9 




Per cent of Ash. 


Nameof Fidd, 


-??..• 


•§.- 


1.- 


"k. 


^- 


^11 




=^ 


e 


etc. 




^' 




C 


C>>i5 


1 


§b^ 


1 


II 


1 


Mall... [Walk 


43.00 


57.00 


48.92 


25.60 


4.27 


1.551 0.G2 


7.63 


5.49 


3.77 


_ 


Pheasant 


70.50 


29. UU 


31.49 35.29 


2.16 


0.471 trace 


3.55 


13.67 


4 93 





Turf 


35.00 


65.00 


48.45 


6.08 


2.75 


1.21 





6.19 


25.71 


5 06 





Queen's Ave.. 
Kitchen Gard. 


44.00 


5f5.0() 


43.75 


6.08 


6,32 


2.00 


trace 


14.45 


15.61 


4.13 





37.00 


63.00 


36.60 


12. a5 


11.20 


trace 


trace 


18.51 


19.60 


7.231 trace 


Satory..[Galy 


33.00 


67.00 


18.70 


24.25 


18.50 


3.72 


0.50 




21.60 


4.651 — 


Clay soil of 


4S.O0 


52.00 


18.75 


45.61 


3.83 


0.95 


1.55 


9.14 


5.00 


7.60 


7.60 


Lime soil, do. 


47.00 


53.00 


17.21 


48.50 


9.00 


trace 





6.21 


5.50 





8.32 


Peat bocr 


40.00 


54.00 


24.43 


30.61 


0.92 


5.15 


trace 


6.06 


8.75 


7,45 




Sand pit 


47.04 


52.06 


22.31 


34.59 


8.10 


1.02 




4.05 


15.58 


6.47 


— 



Here we notice that in almost every instance all the 
mineral ingredients of the plant were extracted from 
these soils by water. Only magnesia and chlorine are in 
any case missing. We are not informed, unfortunately, 
what amount of soluble matters was obtained in these 
experiments. 

We next adduce a number of statements of the pro- 
portion of matters which water is capable of extracting 
from earth, statements derived from the analyses of soils 
of widely differing character and origin. 

I. Very rich soil (excellent for clover) from St. Martin's, 
Upper Austria, treated with six times its quantity of cold 
water (Jarriges). 

II. Excellent beet soil (but clover sick) from Schlan- 
staedt, Silesia, treated with 5 times its quantity of cold 
water (Jarriges). 

III. Fair wheat soil, Seitendorf, Silesia, treated with 5 
times its weight of cold water (Peters). 

lY. Inferior wheat soil from Lampersdorf, Silesia — 
5-fold quantity of water (Peters). 

V. Good wheat soil, Warwickshire, Scotland — 10-fold 
quantity of hot water (Anderson). 

YI. Garden soil, Cologne — 3- fold amount of cold water 
(Grouven). 



AQUEOUS SOLUTION OF THE SOIL. 



311 



Vn. Garden soil, Heidelberg — 3-fold amount of cold 
water (Grouven). 

Vni. Poor, sandy soil, Bickendorf — 3-fold amount of 
cold water (Grouven). 

IX. Clay soil, beet field, Liebesnitz, Bohemia, extract- 
ed with 9.6 times its weight of water (R. Hoffmann). 

X. Peat, Meronitz, Bohemia, extracted with 16 times 
its weight of water (R. Hoffmann). 

XI. Peaty soil of meadow, extracted with 8 times its 
weight of water (R. Hoffmann). 

XH. Sandy soil, Moldau Valley, Bohemia, treated with 
twice its weight of water (R. Hoffmanu). 

XIH. Salt meadow, Stollhammer, Oldeuburg (Harms). 

XIV. Excellent beet soil, Magdeburg (Hellriegel). 

XV. Poor beet soil, but good grain soil, Magdeburg 
(Hellriegel). 

XVI. Experimental soil, Ida-Marienhtitte, Silesia, treat- 
ed with 2|- times its weight of cold water (Kiillenberg). 

XVII. Soil from farm of Dr. Geo. B. Loring, Salem, 
Mass., treated with twice its weight of water (W. G. 
Mixter). 

MATTERS DISSOLVED BY WATER FROil 100,000 P.UITS OF 
VARIOUS SOILS. 





j 


1 

1 


1 


j 




si 

1 




1 


'Hi 


11 


1 


I 


18 


2 


13 


8 


2 


1 


5 


11 


5 


53 


134 


n 


5 


2^ 


3 


51/. 


trace 


trace 


trace 


414 


d/. 


94 


51 


Ill 


6 


1 


4 


4 




trace 


1 


2- 


2 


23 


43 


IV 


10 
34 


trace 


1 

8 


;i 


— 


trace 

7 


1 
9 


11 
22 


3 


18 
3(i 


46 


V 


136 


VI 


17 


3 


9 


71/, 


5 


21/, 


61/, 


131^ 


1 


22 


87 


VII 


23 


IV, 


7 


41/, 


11/, 


11/, 


1 


38 


2 


30 


110 


VTII 


8 


M 


V, 


31/i 


trace 


1 


ll/o 


20 


— 


10 


45 


IX 


33H 


av. 


AK 


9 


5 


31/^3 


18 


trace 





70 


147 


X 


164 

92 

1 


11 ' 

44 

2U 


47 
21 
2 


1 


trace 
trace 
trace 


33 
trace 
trace 


302 

11 

trace 


trace 

1 

trace 


77 
2 


449 
230 
33 


1095 


XI 


425 


XII 


391/^ 


XIII 


79 


43 


16 


476 





407 


144 


58 


, 


170 


1393 


XIV 


19 


3 


3 


5 


1 


4 


4 


20 


3 


88 


150 


XV 


20 


5 


3 


4 


1 


5 


3 


15 


2 


83 


147 


XVI 


61/, 


2 


1 


3 


/2 


51^ 


31/, 


12 


7 


12 


53 


x\ai 


8 


2 


6H 


1 


Mio 


71/2 




1% 


17 


12 


551/2 



312 HOW CROPS FEED. 

The foregoing analyses (all the author has access to 
that are sufficiently detailed for the purpose) indicate 

1. That the quantity of soluble matters is greatest — 400 
to 1,400 in 100,000— in wet, peaty soils (X, XI, XIII), 
though their aqueous solutions are not rich in some of the 
most important kinds of plant-food, as, for example, phos- 
phoric acid. 

2. That poor, sandy soils (Vill, XII) yield to water the 
least amount of soluble matters, — 40 to 45 in 100,000. 

3. That very rich soils, and rich soils especially when 
recently and heavily manured as for the hop and beet 
crops (I, II, V, YI, VII, IX, XIY, XV, XVI), yield, in 
general, to water, a larger proportion of soluble matters 
than poor soils, the quantity ranging in the instances be- 
fore us from 50 to 150 parts in 100,000. 

4. It is seen that in most cases phosphoric acid is not 
present in the aqueous extract in quantity sufficient to be 
estimated ; in some instances other substances, as mag- 
nesia, chlorine, and sulphuric acid, occur in traces only. 

5. In a number of cases essential elements of plant- 
food, viz., phosphoric acid and sulphuric acid, are wanting, 
or their presence was overlooked by the analyst. 

Composition of Drain-Water.— Before further discus- 
sion of the above data, additional evidence as to the kind 
and extent of aqueous action on the soil will be adduced. 
The water of rains, falling on the soil and slowly sinking 
through it, forms solutions on the grand scale, the study 
of which must be instructive. Such solutions are easily 
gathered in their full strength from the tiles of thorough- 
drained fields, when, after a period of dry weather, a rain- 
fall occurs, sufficient to saturate the ground. 

Dr. E. Wolff, at Moeckern, Saxony, made two analyses 
of the water collected in the middle of May from newly 
laid tiles, when, after a period of no flow, the tiles had 



AQUEOFS SOLUTION OF THE SOIL. 



313 



been running full for several hours in consequence of a 
heavy rain. The soil was of good quality. He found : 

IN 100,000 PARTS OF DRAIN-WATER. 





Eye field. 


Meadow. 


Organic matters, 


2.6 


3.2 


Carbonate of lime, 


21.9 


4.4 


" magnesia, 


3.1 


1.4 


" potash, 


0.3 


0.5 


" soda, 


1.9 


1.4 


Cliloride of sodium, 


2.3 


trace 


Sulphate of potash. 


1.3 


trace 


Alumina, 
Oxide of iron, 






0.8 


0.6 


Silica, 


0.7 


0.4 


Phosphoric acid, 


trace 


1.9 



34.8 



13.8 



Prof. Way has made a series of elaborate examinations 
on drain-waters furnished by Mr. Paine, of Farnham, 
Surrey. The waters were collected from the pipes (4-5 
ft. deep) of thorough-drained fields in December, 1855, 
and in most cases were the first flow of the ditches after 
the autumn rains. The soils, with exception of 7 and 8, 
were but a few years before in an impoverished condition, 
but had been brought up to a high state of fertility by ma- 
nuring and deep tillage. {Jour. Roy. Ag. Soc, XYII, 133.) 

IN 100,000 PARTS OF DRAIN-WATER. 



Potash 

Soda 

Lime 

Magnesia 

Oxide of iron and ahimiiia 

Silica 

Chlorine . 

Sulphuric acid 

Phosphoric acid. 

Nitric acid 

Ammonia 

Soluble organic matter 

Total 

14 



1 

Wheat 
field. 



trace 

1.43 

G.93 

0.97 

0.59 

1.35 

1.00 

2.35 

trace 

10.24 
0.025 

10.00 



2 

Hop 
field. 



trace 
3.10 

10.24 
3.31 
0.07 
0.04 
1.57 
7.35 
0.17 

21.05 
0.025 

10.57 



3 
Hop 

field. 



0.03 
3.23 
8.G4 
3.54 
0.14 
0.78 
1.84 
G.28 
trace 
18.17 
0.025 
17.85 



4 
Wheat 
field. 



0.07 

1.24 

2.23 

0.58 

none 

1.71 

1.16 

2.44 

trace 

2.78 

0.017 

8.00 



5 

Wheat 
field. 



trace 

2.03 

3. GO 

0.30 

1.85 

2.57 

1.80 

1.84 

0.11 

4.93 

0.025 

8.14 



34.885 158.095160-525 21.227 I 27.195 39.455 72.979 



6 
Hop 
field. 



0.31 
2.00 
8.31 
1.33 
0.50 
0.93 
1.73 
4.45 
0.09 
11.50 
0.025 
8.28 



7 
Hop 
fi^ld. 



trace 
4.57 

18.50 
3.57 
0.71 
1.21 
3.74 

13.58 
0.17 

16.35 
0.009 

10.57 



314 HOW CROPS FEED. 

Krocker has also published analyses of drain-waters 
collected in summer from poorer soils. He obtained 





IN 100,000 PARTS: 










a 


b 


c 


d 


e 


/ 


Organic matters, 


2.5 


2.4 


1.6 


0.6 


6.3 


5.6 


Carbonate of lime. 


8.4 


8.4 


12.7 


7.9 


7.1 


8.4 


Sulphate of lime. 


20.8 


21.0 


11.4 


1.7 


7.7 


7.2 


Nitrate of lime, 


0.2 


0.2 


0.1 


0.2 


0.2 


0.2 


Carbonate of magnesia, 


7.0 


6.9 


4.7 


2.7 


2.7 


1.6 


Carbonate of iron. 


0.4 


0.4 


0.4 


0.2 


0.2 


0.1 


Potas'h, 


0.2 


0.2 


0.2 


0.2 


0.4 


0.6 


Soda, 


1.1 


1.5 


1.3 


1.0 


0.5 


0.4 


Chloride of Bodimn, 


0.8 


0.8 


0.7 


0.3 


0.1 


0.1 


Silica, 


0.7 


0.7 


0.6 


0.5 


0.6 


0.5 



Total, 42.1 42.5 33.7 . 15.3 25.S 24.7 

Krocker remarks {Jour, far Fraht. Chem.^ 60-466) that 
phosj^horic acid could be detected in all these waters, 
though its quantity Avas too small for estimation. 

a and h are analyses of water from the same drains — a 
gatliered April 1st, and h May 1st, 1853; c is from an ad- 
joining field; d^, from a field where the drains run con- 
stantly, where, accordingly, the drain-water is mixed with 
sj^ring water ; e and f are of water running from the sur- 
face of a field and gathered in the furrows. 

Lysimcter-Water. — Entirely similar results were ob- 
tained by Zuller in the analysis of water which was col- 
lected in the Lysimeter of Fraas. The lysimeter* con- 
sists of a vessel with vertical sides and open above, the 
upper part of which contains a layer of soil (in these ex- 
periments 6 inches deep) supported by a perforated shelf, 
while below is a reservoir for the reception of water. 
The vessel is imbedded in the ground to within an inch of 
its upper edge, and is then filled from the diaphragm up 
with soil. In this condition it remains, the soil in it being 
exposed to the same influences as that of the field, while 
the water which j^ercolates the soil gathers in the reservoir 



Measurer of solution. 



AQFEOUS SOLUTION OF THE SOIL. 815 

below. Dr. Zoller analyzed the water that was thus col- 
lected from a number of soils at Munich, in the half year, 
AprU 7th to Oct. 7th, 1857. He found 

IN 100,000 OF LYSIMETER-WATER: 



Potash, 


0.65 


0.24 


0.20 


0.55 


0.38 


Soda, 


0.71 


0.56 


0.74 


2.37 


0.60 


Lime, 


14.58 


. 5.76 


7.08 


6.84 


9.23 


Magnesia, 


2.05 


0.89 


0.13 


0.29 


0.51 


Oxide of iron. 


0.01 


0.63 


0.83 


0.57 


0.43 


Clilorine, 


5.75 . 


0.95 


2.08 


3.94 


3.53 


Phosplioric acid, 


0.22 


_ 


— 








Sulphuric acid. 


1.75 


2.71 


2.78 


2.93 


3.35 


Silica, ■ 


1.04 


1.13 


1.75 


0.95 


0.93 


Organic matter, with some 


[■20.47 


12.59 


13.67 


12.08 


10.19 


nitric and carbonic acids, 











Total, 47.23 25.46 29.26 30.52 29.15 

The foregoing analyses of drain and lysimeter-water 
exhibit a certain general agreement in their results. 
They agree, namely, in demonstrating the presence in the 
soil-water of all the mineral food of the plant, and while 
the figures for the total quantities of dissolved matters 
vary considerably, their average, 36|- parts to 100,000 of 
water, is probably about equally removed from the ex- 
tremes met with on the one hand in the drainage from a 
very highly manured soil, and on the other hand in that 
where the soil-solution is diluted with rain or spring water^ 

It must not be forgotten that in the analyses of drain- 
age water the figures refer to 100,000 parts of water ; 
whereas, in the an/ilj^ses on p. 311, they refer to 100,000 
parts of soil, and hence the two series of data cannot be 
directly compared and are not necessarily discrepant. 

Is Soil-Water destitute of certain Nutritive Itlatters ? 
— We notice that in the natural solutions which flow ofi" 
from the soil, phosphoric acid in nearly every case exists 
in quantity too minute for estimation ; and when estimat- 
ed, as has been done in a number of instances, its propor- 
tion does not reach 2 parts in 100,000. This fact, together 
with the non-appearance of the same substance and of oth- 



316 HOW CROPS FEED. 

er nutritive elements, viz., chlorine and sulphuric acid, in 
the Table, p. 311, leads to the question. May not the aqueous 
solution of the soil be altogether lacking in some es- 
sential kinds of mineral j)lant-food in certain instances ? 
May it not happen in case of a rather poor soil that it will 
support a moderate crop, and yet refuse to give up to 
water all the ingredients of that crop that are derived 
from the soil ? 

The weight of evidence supports the conclusion that 
water is capable of dissolving from the soil all the sub- 
stances that it contains which serve as the food of plants. 
The absence of one or several substances in the analytical 
statement would seem to be no proof of their actual ab- 
sence in the solution, but indicates simply that the sub- 
stance was overlooked or was too small for estimation by 
the common methods of analysis in the quantity of solu- 
tion which the experimenter had in hand. It Avould ap- 
pear probable that by employing enough of the soil and 
enough water in extracting it, solutions would be easily 
obtained admitting of the detection and estimation of ev- 
ery ingredient. Knop, however, asserts ( Chem. CentraJr 
hlatt^ 1864, 168) that he has repeatedly tested aqueous 
solutions of fruitful soils for phosphoric acid, employing 
the soils in quantities ranging from 2 to 22 lbs., and water 
in similar amounts, without in any case finding any traces 
of it. On the other hand Schulze mentions having inva- 
riably detected it in numerous trials ; and Von Babo, in 
the examination of seven soils, found phosphoric acid in 
every instance but one, which, singularly enough, was 
that of a recently manured clay soil. In no case did ho 
fail to detect lime, potash, soda, sulphuric acid, chlorine, 
and nitric acid ; magnesia he did not look for. {Soff- 
mann's Jahresbericht der Ag. Chem., I. 17.) 

So Heiden, in answer to Knop's statement, found and 
estimated phosphoric acid in four instances in proportions 



AQUEOUS SOLUTION OF THE SOIL. 317 

ranging from 2 to 6 parts in 100,000 of soil. {Jahreabe- 
richt der Ag. Chem., 1865, p. 34.) 

It should be remarked that Knop's failure to find phos- 
phoric acid may depend on the (uranium) method he em- 
ployed, a method different from that commonly used. 

Can the Soil- water supply Crops with Food I— As- 
suming, then, that all the soil-food for plants exists in solu- 
tion in the water of the soil, the question arises, Does the 
water of the soil contain enough of these substances to 
nourish crops ? In case of very fertile or highly manured 
fields, this question without doubt should be answered af- 
firmatively. In respect of poor or ordinary soils, how- 
ever, the answer has been for the most j^art of late years 
in the negative. While to decide such a question is, per- 
haps, impossible, a closer discussion of it may prove ad- 
vantageous. 

Russell {Journal Highland and Ag. /Soc, New Series, 
Vol. 8, p. 534) and Liebig {Ann. d. Chem. u. PJiarm.^ CV, 
138) were the first to bring prominently forward the idea 
that crops are not fed simply from aqueous solutions. Dr. 
Anderson, of Glasgow, presents the argument as follows 
(his Ag. Chemistry^ p. 113) : 

" In order to obtain an estimate of the quantity of the 
substances actually dissolved, we shall select the results 
obtained * by Way. The average rain-fall in Kent, where 
the waters he examined were obtained, is 25 inches. Now, 
it appears that about two-fifths of all the rain which falls 
escapes through the drains, and the rest is got rid of by 
evaporation.! An inch of rain falling on an English acre 
weighs rather more than a hundred tons ; hence in the 
course of a year, there must pass off by the drains about 
1,000 tons of drainage water, carrying with it, out of the 
reach of plants, such substances as it has dissolved, and 



* On drain-waters, see p. 313. 

t From Parke's measurements, Jour. Boy. Ag. Soc., Eng., Vol, XVII, p. 127. 



318 HOW CROPS FEED. 

1,500 tons must remain to give to the plant all that it holds 
in solution. These 1,500 tons of water must, if they have 
the same composition as that which escapes, contain only- 
two and a half pounds of potash and less than a pound 
of ammonia. It may be alleged that the water which re- 
mains lying longer in contact with the soil may contain a 
larger quantity of matters in solution ; but even admit- 
ting this to be the case, it cannot for a moment be sup- 
posed that they can ever amount to more than a very 
small fraction of what is required for a single crop." 

The objection to this conclusion which Anderson al- 
ludes to above, but which he considers to be of little mo- 
ment, is, perliaps, a serious one. The soil is saturated 
with water sufficiently to cause a flow from drains at a 
depth of 4 to 5 ft., for but a small part of the grow- 
ing season. The Indian corn crop, for example, is planted 
in New England in the early part of June, and is harvest- 
ed the first of October. During the four months of its 
growth, the average rain-fall is not enough to make a flow 
from drains for more, perhaps, than one day in seven. 
During six-sevenths of the time, then, there is a current of 
water ascending in the soil to supply the loss by evapora- 
tion at the surface. In this way the solution at the sur- 
face is concentrated by the carrying upward of dissolved 
matters. A heavy rain dilutes this solution, not having 
time to saturate itself before reaching the drains. Ac- 
cordingly we find that the quantity of matters dissolved 
by water acting thoroughly on the surface soil is greater 
than that washed out by an equal amount of drain- water ; 
at least such is the conclusion to be gathered from the 
experiments of Eichhorn and Wunder. 

These chemists have examined the solution obtained by 
leaving soil in contact with Just sufficient water to saturate 
it for a number of days or weeks. ( Ys. St., II, pp. 107- 

111.) 

The soil examined by Eichhorn was from a garden near 



AQUEOUS SOLUTION OF THE SOIL. 319 

Bonn, Prussia, not freshly manured, and was treated with 
about one-third its weight (3G.5 j^er cent) of cold water 
for ten days. 

Wunder employed soil from a field of the Experiment 
Station, Chemnitz, Saxony. This soil had not been re- 
cently manured, and was of .rather inferior quality (yield- 
ed 15 bushels wheat per acre, English). It was also 
treated with about one-third its weight (34.5 per cent) of ^ 
water for four weeks. 

The solutions thus procured contained in 100,000 parts, 

Bonn. Chemnitz. 



Silica, 


4.80 


2.57 


Sulphuric acid, 


10.03 




Pliosphoric acid, 


3.10 


traces 


Oxide of iron and alumina. 


trace 


1.17 


Chloride of sodium, 


5.86 


4.76 


Lime, 


12.80 


8.36 


Magnesia, 


3.84 


3.74 


Potash, 


11.54 


0.75 


Soda, 


1.10 


3.04 



If we assume with Anderson that 1,500 tons (= 3,360,000 
lbs.) of water remain in these soils to feed a crop, and that 
this quantity makes solutions like those whose composition' 
is given above, we have dissolved (in pounds per English 
acre) from the soil of 





Bonn, 


Chemnitz. 


Silica, 


161 


86 


Sulphuric acid. 


343 


— 


Phosphoric acid. 


104 


? 


Oxide of iron and alumina, 




39 


Chloride of sodium. 


197 


160 


Lime, 


430 


281 


Magnesia, 


129 


136 


Potash, 


387 


25 


Soda, 


37 


102 



These results differ widely from those based on the com- 
position of drain-water. Eichhorn, by a similar calcula- 
tion, was led to the conclusion that the soil he operated 
with was capable of nourishing the heaviest crops with 



320 HOW CRors feed. 

its aqueous solution. Wunder, on the contrary, calculat- 
ed that the Chemnitz soil yields insufficient matters for 
the ordinary amount of vegetation ; and we see that as 
respects potash, the wants of grass and root crops could 
not be satisfied with the quantities in our computation, 
while sulphuric acid and phosphoric acid are nearly or en- 
tirely wanting. We do not, however, regard such calcu- 
lations as decisive, either one way or the other. The 
quantity of water which may stand at the actual service 
of a crop is beyond our power to estimate with anything 
like certainty. Doubtless the amount assumed by Ander- 
son is too large, and hence the calculations relative to the 
Bonn and Chemnitz soils as above interpreted^ convey an 
exaggerated notion of the extent of solution. 

Proper Concentration of Plant-Food. — Let us next 
inquire what strength of solution is necessary for the sup- 
port of plants. 

As has been shown by Nobbe ( Vs. St., VIII, p. 337), 
Birner & Lucanus ( Vs. St., YIII, p. 134), and Wolff ( Vs, 
St., YIII, p. 192), various agricultural plants flourish to 
extraordinary perfection when their roots are immersed in 
a solution containing about one part of ash-ingredients 
(together with nitrates) to 1,000 of water. 

The solutions they employed contained the following 
substances in the proportions stated (approximately) be- 



low: 








In 100,000 parts of Water. 


Nobbe. 


Birner & Lucanus. 


Wolff. 


Lime, 


16 


19 


19 


Magnesia, 


3 


6K 


2X 


Potash, 


31 


16 


16 


Phosphoric acid, 


7 


24 


14 


Chlorine, 


21- 


none 


3 


Sulphuric acid, 


6 


13 


4 


Oxide of iron, 


X 


X 


K 


Nitric acid. 


31K 


36 


51 



116 115 109 

Nobbe found further that the visror of vesjetation in his 



AQUEOUS SOLUTION OF THE SOIL. 321 

solution was diminished either by reducing the proportion 
of solid matters below 0.5, or increasing it to 2 parts in 
IjOOO of water. The proper dilution of the food of plants 
for most vigorous growth and most perfect develoj^ment 
is thus approximately indicated. 

We notice, however, considerable latitude as regards 
the jDroportions of some of the most important ingredients 
which are usually present in least quantity in the aqueous 
solution of the soil. Thus, phosphoric acid in one case is 
thrice as abundant as in the other. We infer, therefore, 
that the minimum limit of the individual ingredients is 
not fixed by the above experiments, especially not for or- 
dinary growth. 

Birner and Lucanus communicate other results ( Vs. St., 
yilL, p. 154), which throw much light on the question un- 
der discussion. They compared, the growth of the oat plant, 
when nourished respectively by a rich garden soil, by 
ordinary cultivated land, by a solution the composition 
of which is given above, and lastly by a natural aqueous 
solution of soil, viz., a well-water. Below is a statement 
of the weight in grams of an average plant, produced in 
these various media, as well as that of the grain yielded 
by it. 

Dry crops compared 

Weight of aver- Welfiht of with seed, the latter 

age plant, dry. dry Grain. taken as unity. 

Garden 5.27 ' 1.23 193 

Field 1.75 0.63 64 

Solution 3.75 1.53 137 

Well-water....... 2.91 1.25 106 

We gather from the above figures that well-water, in 
quantities of one quart for each plant, renewed weekly, 
gave a considerably heavier plant, straw, and grain, than 
a field under ordinary culture ; the yield in grain being 
double that of the latter, and equal to that obtained in a 
rich garden soil. 
14* 



322 HOW CROPS FEED. 

The analysis of the well-water shows that the nutritive 
solution need not contain the food of plants in greater 
proj)ortion than occurs in the aqueous extract of ordinary- 
soils. 

The well-water contained, in 100,000 parts. 

Lime, - - - - - 15.14 

Magnesia, 1.53 

Potash, 2.13 

Phosphoric acid, - - - - 0.16 

Sulphuric acid, - - - - 7.45 

Mtric acid, 6.02 

We thus have demonstration that a solution containing 
but one-and-a-half parts of phosphoric acid to ten million 
of water is competent, so far as this substance is concern- 
ed, to support a crop bearing twice as much grain as an 
ordinary soil could produce under the same circumstances 
of weather. Do we thus reach the limit of dilution ? 
We cannot answer for agricultural plants, but in case of 
some other forms of vegetation, the reply is obvious and 
striking. 

Various species of Fucus^ Laminaria^ and other ma- 
rine plants, contain iodine in notable quantities. This 
element, so much used in photography and medicine, is 
made exclusively from the ashes of these sea-weeds, one 
establishment in Glasgow producing 35 tons of it annu- 
ally. The iodine must be gathered from the water of the 
ocean in which these plants vegetate, and yet, although 
the starch-test is so delicate that one part of iodine can 
be detected when dissolved in 300,000 parts of water, it 
is not possible to recognize iodine in the " bitterns " which 
remain when sea-water is concentrated to the one-hund- 
reth of its original bulk, so that its proportion must be 
less than one part in thirty millions of water ! ( Otto's 
Lehrbuch der Chemie, 4te, Ai/fl., pp. 743-4.) 



AQUEOUS SOLUTION OF THE SOIL. 323 

Mode whereby dilute solutions may nourish Crops. — 

There are other considerations which may enable us to 
reconcile extreme dilution of the nutritive liquid of the 
soil, with the conveyance by it into the plant of the req- 
uisite quantity of its appropriate food. It is certain 
that the amount of matters found in solution at any 
given moment in the water of the soil by no means repre- 
sents its power of supplying nourishment to vegetation. 

If the water which has saturated itself with the solu- 
ble matters of the soil be deprived of a portion or all of 
these matters, as it might be by the absorptive action of 
the roots of a plant, the water would immediately act 
anew upon the soil, and in time would dissolve another 
similar quantity of the same substance or substances, and 
these being taken up by plants, it would again dissolve 
more, and so on as long and to such an extent as the soil 
itself would admit. In other words, the same watey^ may 
act over and over again in the soil, to transfer from it to 
the crop the needful soluble matters. It has been shown 
that the substances dissolved in water may diffuse through 
animal and vegetable tissues independently of each other, 
and independently of the water itself. (H. C. G., p. 340.) 

Deportment of the Soil to renewed portions of Water. 
— ^It remains to satisfy ourselves that the soil is capable 
of yielding soluble matters continuously to renewed por- 
tions of water. The only observations on this point that 
the writer is acquainted with are those made by Schulze 
and Ulbricht. Schulze experimented on a rich soil from 
Goldberg, in Mecklenburg ( Vs. St., VI., 411). This soil, 
in a quantity of 1,000 grams (= 2.2 lbs.) was slowly 
leached with pure water, so that one liter (= 1.056 quart) 
of liquid passed it in 24 hours. The extraction was con- 
tinued during six successive days, and each portion was 
separately examined for total matters dissolved, and for 
phosphoric acid, which is, in general, the least soluble of 
the soil-ingredients. 



324 



HOW CEOPS FEED. 



The results were as follows, for 1,000 parts of extract, 



Portion of 
aqueous 
extract. 


Total 

matters 

dissolved. 


Organic 

and 
Tolatile. 


Inorganic. 


Phosphoric 
acid. 


1 


0.535 


0.340 


0.195 


0.0056 


2 


0.120 


0.057 


0.063 


0.0082 


3 


0.261 


0.101 


0.160 


0.0088 


4 


0.203 


0.083 


0.120 


0.0075 


5 , 


0.260 


0.082 


0.178 


0.0069 


6 


0.200 


0.077 


0.123 


0.0044 



1.579 



0.740 



0.839 



0.0414 



We see tliat each successive extraction removed. from 
the soil a scarcely diminished quantity of mineral mat- 
ters, including phosphoric acid. In case of a poor soil, 
we should not expect results so striking, as regards quan- 
tity of dissolved matters, but doubtless they would be 
similar in kind. 

This is shown by the investigations that follow. 

Ulbricht gives ( Vs. JSL^ V., 207) the results of the simi- 
lar treatment of four soils. 1,000 grams of each were 
put in contact with four times as much pure water for 
three days, then two-thirds of the solution was poured off 
for analysis, and replaced by as much pure water; this 
was repeated ten times. Partial analyses were made of 
some of the extracts thus obtained ; we subjoin the pub- 
lished results : 



Dissolved by 40,000,000 parts of water from 1,000,000 parts of— 
Loamy Sand from Heiusdorf. 





1st 
Extract. 


2d 
Extract. 


3d 
Extract. 


4th 
Extract. 


7th 
Extract. 


10th 
Extract. 


Potash 


30K 
34 
95 

301^ 
trace. 


15 
14 
39 
12 

IK 


15 
21 
38 
10 
3 


8 
18 
39 
10 

3 




4 


Soda 


11 


Lime 




Magnesia 




Phosphoric acid... 




Total 


190 


81K 


87 


78 







AQUEOUS SOLUTION OF THE SOIL. 



325 







Loamy Sand fr 


om "Wahlsdorf. 




Potash 


23 

26 

116 

36>^ 


12 
16 
43 
15 
3 


13 
20 
39 
14 
4 


6 
16 
43 
13 

4 


48 
14 


4 


Soda 


6 


Lime 








Phosphoric acid.. 




Total 


208K 


89 


90 


80 


















Loamy ferruginous Sand from Dahmc, containing 4)^ 
of liumus. 


Potash. 


7 

41 

96 

14 

trace. 


6 

11 

70 

30 

2 


7 7 


03 

8 


3 


Soda 


26 
55 

trace. 


17 

48 

7 

1 


8 


Lime 




Magnesia 

Phosplioric acid.. 




Total 


15S 


99 


97 


80 




















Fine Sandy Loam from Fallcenberg. 


Potash 


15 
47 
47 
17 
3 


11 
12 

27 
8 
2 


9 
13 
19 

5 

trace. 


9 

8 
18 
6 
trace. 






Soda. . . . 




Lime 








Phosphoric acid.. 




Total 


129 


60 


45 


41 







As Schulze remarks, it is practically imi^ossible to ex- 
haust a soil completely by water. This liquid will still 
dissolve something after the most prolonged or frequently 
renewed action, as not one of the components of the soil 
is possessed of absolute insolubility, although in a sterile 
soil the amount of matters taken up would presently be- 
come what the chemist terms " traces," or might be such 
at the outset. 

The two analyses by Krocker, a and 5, p. 314, made 
on water from the same drain, gathered at an interval of 
one month, further show that water, rapidly percolating 
the soil, continuously finds and takes up new portions of 
all its ingredients. 

In addition to the simple solution of matters, the soil 
suffers constantly the chemical changes which have been 
already noticed, and are expressed by the term weather- 



326 HOW CROPS FEED. 

ing. Matters insoluble in water to-day become soluble 
to-morrow, and substances that to-morrow resist the action 
of water are taken up the day after. In this way there 
is no limit to the solution of the soil, and we cannot there- 
fore infer from what the soil yields to water at any given 
moment nor from what is taken out of it by any given 
amount of water, the real extent to which aqueous action 
operates, during the long period of vegetable growth, to 
present to the roots of a crop the indispensable ingredi- 
ents of its food. 

The discussion of the question as to the capacity of 
water to dissolve from the soil enough of the various in- 
gredients to feed crops, while satisfactorily establishing 
this capacity in case of rich soils, and making evident 
that in poor soils most of the inorganic matters are pre- 
sented to vegetation by water in sufficient quantity, does 
not entirely satisfy us in reference to some of the needful 
elements of the j^lant, especially phosphoric acid. 

It is therefore appropriate, in this place, to pursue fur- 
ther inquiries into the mode by which vegetation acquires 
food from the soil, although to do so will somewhat inter- 
rupt the general plan of our chapter. 

Direct action of Roots upon the Soil. — In noticing 

the means by which rocks are converted into soils, the 
action of the organic acids of the living plant has been 
mentioned. Since that chapter was written, further evi- 
dence has been obtained concerning the influence of the 
plant on the soil, which we now proceed to adduce. 

Sachs {Experimental Physiologie^ 189) gives an ac- 
count of observations made by him on the action of roots 
on marble, dolomite (carbonate of lime and magnesia), 
magnesite (carbonate of magnesia), osteolite (phosphate 
of 'lime), gypsum, and glass. Polished plates of these 
substances were placed at the bottom of suitable vessels 
and covered several inches in depth with fine quartz sand. 
Seeds of various plants were planted in the sand and kept 



DIRECT ACTION OF ROOTS UPON THE SOIL. 327 

moist. The roots penetrated the sand and came in con- 
tact with the plates below, and branched horizontally on 
their surfaces. After several days or weeks the plates 
were removed and examined. The plants employed were 
the bean, maize, squash, and wheat. The carbonates of 
lime and magnesia and the phosphate of lime were plain- 
ly corroded where they had been in contact with the 
roots, so that the course of the latter could be traced with- 
out difficulty. Even the action of the root-hairs was mani- 
fest as a faint roughening of the surface of the stone 
either side of the path of the root. Gypsum and glass 
were not perceptibly acted on. 

Dietrich has made a series of experiments {Hoffmann^ s 
Jahreshericlit^ YI, 3) on the amount of matters made solu- 
ble from basalt and sandstone, both coarsely powdered, 
and kept watered with equal quantities of distilled water, 
when supporting and when free from vegetation. The 
crushed rocks were employed in quantities of 9 and 11 
lbs. ; they were well washed before the trials with dis- 
tilled water, and access of dust was prevented by a layer 
of cotton batting upon the surface. After removing the 
plants, at the termination of the experiments, each sam- 
ple of rock-soil was washed with the same quantity of 
water, to which a hundredth of nitric acid had been 
added. It was found that the plants employed, especially 
lupins, peas, vetches, spurry, and buckwheat, assisted in 
the decomposition and solution of the basalt and sand- 
stone. Not only did these plants take up mineral mat- 
ters from the rock, but the latter contained besides, a 
larger amount of soluble matters than was found in the 
experiments where no plants were made to grow. The 
cereal grains had the same effect, but in less degree. In 
the subjoined table we give the total quantities of sub- 
stances dissolved under the influence of the growing 
vegetation. These figures were obtained by adding to 
what was found in the washinQ:s of the rock-soils the ash 



On 9 lbs. of 
sandstone. 


On 11 lbs. of 
basalt. 


0.608 grams. 
0.481 " 
0.268 " 


0.749 grams. 
0.713 " 
0.365 " 


0.233 " 
0.231 " 


0.337 " 
0.351 " 


0.027 " 
0.014 " 


0.196 " 
0.132 " 



328 HOW CROPS TEED* 

of the crops, and subtracting from tliat sum the ash of 
the seeds, together with the matters made soluble in the 
same soils, which had sustained no plants, but which had 
been treated otherwise in a similar manner. 

MATTERS DISSOLVED BY ACTION OF ROOTS. 



Of 3 lupin plants 0.608 grams 

3 pea " 

20 spurry " 

10 buckwh't " 

4 vetch " 

8 wheat " 

8 rye " 

These trials appear to show conclusively that plants 
exert a decided effect on the soil. We are not informed, 
however, what particular substances are rendered soluble 
under this influence. 

We conclude, then, that the direct action of the roots 
of a crop may in all cases contribute toward supplying it 
with food, and in many instances may be absolutely 
essential to its satisfactory growth. 

Further Notice of Matters Soluble in Water.— The 

analyses we have quoted show that every chemical ele- 
ment of the soil may pass into aqueous solution. They 
also show that some substances are dissolved more easily 
and in greater quantity than others. 

In general, chlorine, nitric acid, and sulphuric acid, 
are most readily and completely taken up by w^ater, and, 
for the most part, in combination with lime, soda, and, 
magnesia. In some cases, sulphuric acid appears to exist 
in a difficultly soluble condition ( Van Bemmelen, Ys, 
St., yilL, 263). 

Potash, ammonia, oxide of iron, alumina, silica, and 
phosphoric acid, are the substances which are usually 
soluble in but small proportion. These, together with 



ACID SOLUTIOIf OF THE SOIL. 329 

lime, magnesia, and soda, it is difficult or impossible to 
wash put completely from, a soil of good quality. 

Very poor soils may be deficient in soluble forms of 
any or several of the above ingredients, and therefore 
readily admit of nearly complete extraction by a small 
amount of water. 

Certain soils contain soluble salts of iron and alumina 
(sulphates and humates) in considerable quantity, and 
are for that reason unproductive. Such are many marsh 
lands, as well as upland soils containing bisulphide of iron 
(iron pyrites), of the kind that readily oxidizes to sulphate 
of protoxide of iron (copperas). 

§3. 

SOLUTION OF THE SOIL IN STRONG ACIDS. 

The strong acids, hydrochloric (muriatic), nitric, and 
sulphuric, by virtue of their vigorous affinities, readily 
remove from the soil a considerable quantity of all its 
mineral ingredients. The quantity thus taken up is 
greatly more than can be dissolved in water, and is, in 
general, the greater, the more fertile the soil. Exceptions 
are soils consisting largely of carbonate of lime (chalk 
soils), or compounds of iron (ochreous soils). The diffisr- 
ent acids above named exercise very unlike solvent effects 
according to their concentration, the time of their action, 
the temperature at which they are applied, and the chemi- 
cal nature and state of division of the soil. 

The deportment of the minerals which chiefly constitute 
the soil towards these acids will enable us to under- 
stand their action upon the soil itself. Of these minerals 
quartz, feldspar, mica, hornblende, augite, talc, steatite, 
kaolinite, chrysolite, and chlorite, when not altered by 
weathering, nearly or altogether resist the action of even 
hot and moderately strong hydrochloric and nitric acids. 



830 now CKOPS feed. 

On the other hand, all carbonates, sulphates, and phos- 
phates, are completely dissolved, while the zeolites and 
serpentine are decomposed, their alkalies, lime, etc., enter- 
ing into solution, and the silica they contain separating, for 
the most part, as gelatinous hydrate. 
, According to the nature of the soil, and the concentra- 
tion of the reagent, hydrochloric acid, the solvent usually 
employed, takes up from two to fifteen or more per cent. 
Very dilute acids remove from the soil the bases, lime, 
magnesia, potash, and soda, in scarcely greater quantity 
than they are united with chlorine, and with sulphuric, 
phosphoric, carbonic, and nitric acids. Treatment with 
stronger acids takes up the bases above mentioned, par- 
ticularly lime and magnesia, in greater proportion than 
the acids specified. We find that, by the stronger acids, 
silica is displaced from combination (and may be taken 
up by boiling the soil with solution of soda after treat- 
ment with the acid). It hence follows that silicates, such 
as are decomposable by acids, (zeolites) exist in the soil, 
although we cannot recognize them directly by inspec- 
tion even with the help of the microscope. To this point 
we shall subsequently recur. 

§ 4. 
PORTION OF SOIL INSOLUBLE IN ACIDS. 

When a soil has been boiled with concentrated hydro- 
chloric acid for some time, or until this solvent exerts no 
further action, there may remain quartz, feldspar, mica, 
hornblende, augite, and kaolinite (clay), together with 
other similar silicates, which, in many cases, are ingredients 
of the soil. Treatment with concentrated sulphuric acid 
at very high temperatures (Mitscherlich) , or syrupy phos- 
phoric acid (A. Mtiller), decomposes all these minerals, 
quartz alone excepted. By making, therefore, in the first 



CHEMICAL ACTION IN THE SOIL. 331 

place, a meclianical analysis, as described on page 147, and 
subjecting the fine portion, which consists entirely or in 
great part of clay, to the action of these acids, the quan- 
tity of clay may be approximately estimated. Or, by 
melting the portion insoluble in acids with carbonate of 
soda, or acting upon it with hydrofluoric acid, the whole 
may be decomposed, and its elementary composition be 
ascertained by further analysis. 

Notwithstanding an immense amount of labor has been 
expended in studying the composition of soils, and chiefly 
in ascertaining what and how much, acids dissolve from 
them, we have, unfortunately, very few results in the way 
of general principles that are of application, either to a 
scientific or a practical purpose. In a number of special 
cases, however, these investigations have proved exceed- 
ingly instructive and useful. 

§5. 

REACTIONS BY WHICH THE SOLUBILITY OF THE ELEMENTS 
OF THE SOIL IS ALTERED. SOLVENT EFFECT OF 
VARIOUS SUBSTANCES THAT ARE COMMONLY 
BROUGHT TO ACT UPON SOILS. THE AB- 
SORPTIVE AND FIXING POWER OF SOILS. 

Chemical Action in the Soil, — Chemistry has proved 
that the soil is by no means the inert thing it appears to 
be. It is not a passive jumble of rock-dust, out of which 
air and water extract the food of vegetation. It is not 
simply a stage on which the plant performs the drama of 
growth. It is, on the contrary, in itself, the theater of 
ceaseless activities ; the seat of perpetual and complicated 
changes. 

A large share of the rocks now accessible to our study 
at the earth's surface have once been soil, or in the condi- 
tion of soil. Not only the immense masses of stratified 
limestones, sandstones, slates, and shales, that cover so 



332 HOW CKOPS FEED. 

large a part of the Middle States, but most of the rocks 
of New England liave been soil, and have supported vege- 
table and animal life, as is proved by the fossil relics that 
have been disinterred from them. 

We have explained the agencies, mechanical and chemi- 
cal, by which our soils have been formed and are forming 
from the rocks. By a reverse metamorphosis, involving 
also the cooperation of mechanical and chemical and even 
of vital influences, the soils of earlier ages have been so- 
lidified and cemented to our rocks. IsTor, indeed, is this 
process of rock-making brought to a conclusion. It is 
going on at the present day on a stupendous scale in vari- 
ous parts of the world, as the observations of geologists 
abundantly demonstrate. If we moisten sand with a so- 
lution of silicate of soda or silicate of potash, and then 
drench it with chloride of calcium, it shortly hardens to 
a rock-like mass, possessing enough firmness to answer 
many building purposes (Ransome's artificial stone). A 
mixture of lime, sand, and water, slowly acquires a simi- 
lar hardness. Many clay-limestones yield, on calcination, 
a material (water-lime cement) which hardens speedily, 
even under water, and becomes, to all intents, a rock. 
Analogous changes proceed in the soil itself. Hard pan, 
which forms at the plow-sole in cultivated fields, and 
moor-bed pan, which makes a j^eat basin impervious to 
water in beds of sand and gravel, are of the same nature. 

The bonds which hold together the elements of feldspar, 
of mica, of a zeolite, or of slate, may be indeed loosened 
and overcome by a superior force, but they are not de- 
stroyed, and reassert their power when the proper cir- 
cumstances concur. The disintegration of rock into soil 
is, fgr the most part, a slow and unnoticed change. So, 
too, is the reversion of soil to rock, but it nevertheless 
goes on. The cultivable surface of the earth is, however, 
on the whole, far niore favorable to disintegration than 
to petrifaction. Nevertheless, the chemical affinities and 



ABSORPTIVE POWER OF THE SOIL. 33o 

physical qualities that oppose disintegration are inherent 
in the soil, and constantly manifest themselves in the 
kind, if not in the degree, involved in the making of rocks. 
The fourteen elementary substances that exist in all soils 
are capable of forming and tend to form a multitude of 
combinations. In our enumeration of the minerals from 
which soils originate, we have instanced but a few, the 
more common of the many which may, in fact, contribute 
to its formation. The mineralogist counts by hundreds 
the natural compounds of these very elements, com- 
pounds which, from their capability of crystallization, 
occur in a visibly distinguishable shape. The chemist is 
able, by putting together these elements in different pro- 
portions, and under various circumstances, to identify a 
further number of their compounds, and both mineralogy 
and chemistry daily attest the discovery of new combi- 
nations of these same elements of the soil. 

We cannot examine the soil directly for many of the 
substances which most certainly exist in it, on account of 
their being indistinguishable to the eye or other senses, 
even when assisted by the best instruments of vision. 
We have learned to infer their existence either from analo- 
gies with what is visibly revealed in other spheres of ob- 
servation, or from the changes we are able to bring about 
and measure by the art of chemical analysis. 

Absorptive Power of the Soil. — We have already 
drawn attention to the fact that various substances, when 
put in contact with the soil, in a state of solution in water, 
are withdrawn from the liquid and held by the soil. As 
has been mentioned on p. 175, the first appreciative rec- 
ord of this fact appears to have been published by 
Bronner, in 1836. In his work on Grape Culture occur 
the following passages : " Fill a bottle which has a small 
liole in its bottom with fine river sand or half-dry sifted 
garden earth. Pour gradually into the bottle thick and 
putrefied dung-liquor until its contents are saturated. The 



334 HOW CKOPS PEED. 

liquid that flows out at the lower opening appears almost 
odorless and colorless, and has entirely lost its original 
properties." After instancing the facts that wells situ- 
ated near dung-pits are not spoiled by the latter, and that 
the foul water of the Seine at Paris becomes potable af- 
ter filtering through porous sandstone, Bronner contin- 
ues : " These examples sufficiently prove that the soil, 
even sand, possesses the property of attracting and fully 
absorbing the extractive matters so that the toater which 
subsequently passes is not able to remove thetn / even the 
soluble salts are absorbed^ and are only washed out to a 
small extent by nev) quantities of waterP 

It was subsequently observed in the laboratory of 
Liebig, at Giessen, that w^ater holding ammonia in solu- 
tion, when poured upon clay, ran through deprived of 
this substance. AfterAvard, Messrs. Thompson and Hux- 
table, of England, repeated and extended the observa- 
tions of Bronner, and in 1850, Professor Way, then 
chemist to the Roy. Ag. Soc. of Eng., published in the 
Journal of that Society, Vol. XL, pp. 313-879 an account 
of a most laborious and fruitful investigation of the sub- 
ject. Since that time many chemists have studied the 
phenomena of absorption, and the results of these labors 
will be briefly stated in the paragraphs that follow. 

There are two kinds of absorptive power exhibited by 
soils. One is purely physical, and is the consequence of 
adhesion or surface-attraction, exerted by the particles of 
certain ingredients of the soil. The other is a chemical 
action, and results from a play of affinities among certain 
of its components. 

The physical absorptive power of various bodies, in- 
cluding the soil, has been already noticed in some detail 
(pp. 161-176). In experiments like those of Bronner, 
just alluded to, the absorption of the coloring and odor- 
ous ingredients of dung-liquor is doubtless a physical 
process. These substances are separated from solution by 



ABSORPTIVE POWER OF THE SOIL. 335 

the soil just as a mass of clean wool separates indigo from 
the liquor of a dye-vat, or as bone-charcoal removes the 
brown color from syrup. 

Chemical absorptions depend upon the formation of 
new compounds, and in many cases occasion chemical 
decompositions and displacements in such a manner that 
while one ingredient is absorbed, and becomes in a sense 
fixed, another is released from combination and becomes 
soluble. Brief notice has already been made of the 
chemical absorption of ammonia by the soil (p. 243). 
We shall now enter upon a fuller discussion of this and 
allied phenomena. 

When solutions of the various soluble acids and bases 
existing in the soil, or of their salts, are put in contact 
with any ordinary earth for a short time, suitable exami- 
nation proves that in most cases a chemical change takes 
place, — a reaction occurs between the soil and the 
substance. 

If we provide a number of tall, narrow lamp-chimneys 
or similar tubes of glass, place on the flanged end of each 
a disk of cotton-batting, tying over it a piece of muslin, 
then support them vertically in clamps or by strings, and 
fill each of them compactly, two-thirds full of ordinary 
loamy soil, which should be free from lumps, we have an 
arrangement suitable for the study of the absorptive 
power in question. 

Let now solutions, containing various soluble salts 
of the acids and bases existing in the soil, be pre- 
pared. These solutions should bo quite dilute, but 
still admit of ready identification by their taste or by 
simple tests. We may employ, for example, any or all of 
the following compounds, viz., saltpeter, common salt, sul- 
phate of magnesia, phosphate of soda, and silicate of soda. 

If we pour solution of saltpeter on the soil, which 
should admit x)f its ready but not too rapid percolation, 
we shall find that the first portions of liquid which pass 



836 HOW CKOPS FEED. 

are no longer a solution of nitrate of potash, but one of 
nitrates of lime, magnesia, and soda. The potash has 
disappeared from solution* and become a constituent of 
the soil, while other bases, chiefly lime, have been dis- 
placed from the soil, and now exist in the solution with 
the nitric acid. 

If we operate in a similar manner on a fresh tube 
of soil with solution of salt (chloride of sodium), we 
shall find by chemical examination that the soda of the 
salt is absorbed by the soil, while the chlorine passes 
through in combination with lime, magnesia, and potash. 
In case of sulphate of magnesia, magnesia is retained, and 
sulphates of lime, etc., pass through. With phosphates 
and silicates we find that not only the base, but also these 
acids are retained. 

Law of Absorption and Displacement. — ^From a great 

number of experiments made by Way, Liebig, Brustlein, 
Henneberg and Stohmann, Rautenberg, Peters, Weinhold, 
Ktillenberg, Heiden, Knop, and others, it is established 
as a general fact that all cultivable soils are able to de- 
compose salts of the alkalies and alkali earths in a state 
of solution, in such a manner as to retain the base together 
with phosphoric and silicic acids, while chlorine, nitric 
acid, and sulphuric acid, remained dissolved, in union with 
some other base or bases besides the one with which they 
were originally combined. The absorptive power of the 
soil is, however, limited. After it has removed a certain 
quantity of potash, etc., from solution its action ceases, it 
has become saturated, and can take up no more." If, 
therefore, a large bulk of solution be filtered through a 
small volume of earth, the liquid, after a time, passes 
through unaltered. 



* The absence of potash may be shown by aid of strong, cold solution of 
tartaric acid, wliich will precipitate bitartrate of potash (cream of tartar) from 
the original solution, if not too dihite, but not from that which has filtered 
through the soil. The presence of lime in the liquid that passes the soil may be 
Bhown by adding to it either carbonate or oxalate of ammonia. 



ABSORPTIVE POWER OF THE SOIL. 337 

Experiments to ascertain 7iow much of a substance the soil is able to 
absorb are made by putting a known amount of the dry soil (e. g. 100 
grms.) in a bottle with a given volume (e. g. 500 cubic cent.) of solution 
whose content of substance has been accurately deteimined. The solu- 
tions are most conveniently prepared so as to contain as many grms. of 
the salt to the liter of water as corresponds to the atomic weight or 
equivalent of the former, or one-half, one-tenth, etc., of that amount. 
The soil and solution arc kept in contact with occasional agitation for 
some hours or days, and then a measured portion of the liquid is 
filtered off and subjected to chemical analysis. 

The absorptive power of the soil is exerted unequally 
towards individual substances. Thus, in Peters' exj^eri- 
ments ( Vs. St.^11.^ 140), the soil he operated with absorb- 
ed the bases in quantities diminishing in the following 
order : 

Potash, Ammonia, Soda, Magnesia, Lime. 

Another soil, experimented upon by Kiillenberg 
{Jahreshericht iiher Agricultur. Chemie^ 1865, p. 15), ab- 
sorbed in a different order of quantity, as follows : 
Ammonia, Potash, Magnesia, Lime, Soda. 

As might be expected, different soils exert absorptive 
power tovmrds the same substance to an unequal extent. 
Rautenberg {Henneberg's Jour, filr JLandwirthschaft, 
1862, p. 62), operated with nine soils, 10,000 parts of which, 
under precisely similar circumstances, absorbed quantities 
of ammonia ranging from 7 to 25 parts. 

The time required for absorption is usually short. 
Way found that in most cases the absorption of ammonia 
was complete in half an hour. Peters, however, observed 
that 48 hours were requisite for the saturation of the soil 
he employed with potash, and in the experiments of Hen- 
neberg and Stohmann {Henneberg' s Journcd^ 1859, p. 35), 
phosphoric acid continued to be fixed after the expiration 
of 24 hours. 

The strength of the solution influences the extent of 
absorption. The stronger the solution., the more suhstance 
is taken up from it by the soil. Thus, in Peters' experi- 
15 



338 HOW CRors feed. 

ments, 100 grms. of soil absorbed from 250 cubic centi- 
meters of solutions of chloride of potassium of various 
degrees of concentration, as follows : 

strength of Solution. Potash absorbed by 

Besigna- Quantity of potash in 250 c.c. 100 parts By 10,000 parts in Proportum 

tion. of solution. of soil, round numbers. absorbed. 

equiv. = 0.1472 gram. 0.9888 gram. 10 ^U 



Uo " = 0.2944 

loo " = 0.5888 

1,0 " = l-HT? 

!fi " = 2.3555 



0.1381 " 14 i|2 

0.1990 " 20 Ma 

0.3124 " 31 M4 

0.4503 " 45 Ms 



A glance at the right-hand column shows that although 
absolutely less potash is absorbed from a weak solution 
than from a strong one, yet the weak solutions yield 
relatively more than those which are concentrated. 

The quantity of base absorbed in a given time, also de- 
pends upon the relative mass of the solution and soil. In 
these experiments Peters treated a soil with various bulks 
of ^l^o solution of chloride of potassium. The results are 
subjoined : — 

From 250 c.c. of solution 10,000 parts of soil absorbed 20 parts. 
500 " " ' " " " " " " 25 " 

" 1,000 '* " " " " " " " 29 " 

The quantity of a substance absorbed by the soil de- 
pends somewhat on the state of comhi7iatlon it is in, i. e., 
on the substances with which it is associated. Peters 
found, for example, that 10,000 parts of soil absorbed from 
solutions of a number of potash-salts, each containing 
^1^3 of an equivalent of that base expressed in grams, to 
the liter, the following quantities of potash : — 
From phosphate, 49 parts. 

" hydrate, 40 " 

" carbonate, 82 " 

" bicarbonate, 28 " 

" nitrate, 25 " 

" sulphate, 21 " 

" chloride* and carbonate, 21 " 
" chloride, 20 « 

* Chloride of Potassium, KCl. 



ABSOEPTIVE POWER OF THE SOIL. 339 

We observe that potash was absorbed in this case in 
largest proportion from the phosphate, and in least from 
the chloride. Henneberg and Stohmann, operating on a 
garden soil, observed a somewhat different deportment of 
it towards ammonia-salts. 10,000 parts of soil absorbed 
as follows : — 

From phosphate, 21 parts. 

" hydrate, 13 " 

sulphate, 12 " 

hydrate and chloride,* 11^ 1^ " 
chloride, 11 

nitrate, 11 " 

Fixation neither complete nor permanent. — A point 
of the utmost importance is that noue of the bases are 
ever completely absorbed even from the most dilute solu- 
tions. Liebig indeed, formerly believed that potash is en- 
tirely removed from its solutions. We find, in fact, that 
when a dilute solution of potash is slowly filtered through 
a large body of soil, the first portions contain so little of 
this substance as to give no indication to the usual tests. 
These portions are similar in composition to drain-waters, 
and like the latter they contain potash in very minute 
though appreciable quantity. 

In accordance with the above fact, it is found that water 
will dissolve and rerflove a portion of the potash, etc., 
which a soil has absorbed. 

Peters placed in 250 c.c. of a solution of chloride of 
potassium 100 grams of soil, which absorbed 0.2114 gram 
of potash. At the expiration of two days, one-half of the 
solution was removed, and its place was supplied with 
pure water. After two days more, one-half of the liquid 
was again removed, and an equal volume of water added; 



Chloride of Ammonium, Nn4Cl. 



340 



HOW CROPS FEED. 



and this process was repeated ten times. The soil lost 
thus in the several washin2:s as follows : 



In 2d, 


3d, 


4th, 


5th, 


6th, 7th extract. 


0.0075 


0.0096 


0.0082 


0.0069 


0.0075 0.0082 grams. 






In Sth, 


9th, 


10th extract. 






0.0112 


0.0201 


0.083 grams. 



Removed in all, 0.0875 gram of potash. 
Remained in soil, 0.1239 gram. 

In these experiments one part of absorbed potash re- 
quired 28,100 parts of water for solution. 

Similar results were obtained by Henneberg and Stoh- 
mann with a soil which had absorbed ammonia ; one part 
of this base required 10,000 parts of water for re-solution. 

It has been already stated, that the absorption of one 
base is accompanied hy the liberation of a corresponding 
quantity of other hases^ while the acid element, if it be 
sulphuric or nitric acid, or chlorine, is found in its 
orlgincd quantity in the solution. As an illustration of 
this rule, the following data obtained by Weinhold in the 
treatment of a soil with sulphate of ammonia are ad- 
duced. The quantities are expressed in grams, except 
where otherwise stated. 

Content of Solution 



before 
contact with tJie soil. 



'k^.. 



^'s 



300 0.303 0.129 
200 0.455 0.193 






after 
contact tvith the soil. 



to S 



0.329 

0.488 



1-^ 



0.056 
0.120 



0.012 
0.011 



0.121 
0.034 



0.110 
0.105 



0.049 
0.0.30 



We observe that the soil not only retained no sulphuric 
acid, but gave up a small quantity to the solution. Of 
the ammonia a little more than one-half in one case, and 
three-eighths in the other, was absorbed, and in the solu- 
tion its place was supplied chiefly by lime, but to some 
extent also by potash, soda, and magnesia, which were 
dissolved from the soil. It is also to be noticed that in 
the two cases — unlike quantities of the same soil and 






ABSOEPTrVE POWER OF THE SOIL. 



341 



solution having been employed — the bases were displaced 
in quantities that bear to each other no obvious relation. 

Another fact which follows from the rule just illustra- 
ted, is the following : Any base that has been absorbed by 
the soil, may be released from combination partly or en- 
tirely by any other. 

Peters subjected a soil which had been saturated with 
potash and subsequently washed copiously with water to 
the action of various solutions. The results, which exhib- 
it the principle just stated, are subjoined. The soil was 
employed in portions of 100 grams, each of which con- 
tained 0.204 gram of absorbed potash. These were di- 
gested for three days with 250 c.c. of solutions (of ni- 
trates) of the content below indicated. 

For sake of comparison the amount of matters taken up 
by distilled water is added. 





Dissolved by the solution. 




Content of 
solution. 


Lime. 


Magne- 
sia. 


Potash. 


Soda. 


Am7no- 
nia. 


Absorbed 
bij the soil. 


gram. 
0.2808 soda. 
0.2165 ammonia. 
0.2996 lime. 
2317 magnesia. 
Dist. water. 


0.0671(?) 
0.0322 
0.2380 
0.0S12 
trace 


0.0006 

0.0020 
0.1726 


0.0983 
0.1455 
0.1252 
0.1224 
0.0434 


0.2197 
0.0024 
0.0252 
0.0245 
0.0004 


0.1596 


0.0611 soda. 
0.05G9 ammonia. 
0.0616 lime, 
j 0.0591 magnesia. 



We notice that while distilled water dissolved about ^ \^ 
of the absorbed potash, the saline solutions took up two, 
three, or more times that quantity. We observe further 
that soda liberated lime and magnesia, ammonia liberated 
lime and soda, lime brought into solution magnesia and 
soda, and magnesia set free lime and soda from the soil 
itself 

Again, Way, Brustlein, and Peters, have shown in case 
of various soils they experimented with, that the satura- 
ting of them with one base (potash and lime were tried) 
increases the absorbent poioer for other bases, and on the 
other hand, treatment with acids, which removes absorbed 
bases, diminishes their absorptive power. 



342 



HOW CROPS FEED. 



This fact is made evident by the following data furnish- 
ed by Peters. The soils employed were 

ISTo. 1. Unaltered Soil. 

No. 2. Soil heated with hydrochloric acid for some 
time, then thoroughly washed with water. 

'No. 3. No. 2, boiled with 10 grams of sulphate of hme 
and water, and washed. 

No. 4. No. 2, boiled with solution of 10 grams of chlo- 
ride of calcium, and well washed with water. 

No. 5. No. 2, boiled with water and 10 grams of car- 
bonate of lime. 

No. 6. No. 2, boiled with solution of bicarbonate of 
lime, and washed. 

Portions of 100 grams of each of the above were placed 
in contact with 250 c.c. of ' |,„ solution of chloride of po- 
tassium for three days. The results are subjoined: 



Number 


Dissolved by the solution. 


Potash absorbed 
by the soil. 


of soil. 


Lime. 


Magnesia. 


Soda. 


CJiIorine. 


1 

2 


0.0940 
0.0136 
0.0784 
0.0560 
0.1176 
0.1456 


0.0084 


0.0261 
0.0004 
0.0019 
0.0024 
0.0019 


0.4482 
0.4444 
0.4452 
0.4452 
0.4425 
0.4404 


0.1841 


3 

4 

5 

6 


0.0024 
0.0094 
0.0094 
0.0074 


0.0227 
0.0882 
0.1243 
0.1378 
0.2011 



It is seen that the soil which had been washed with 
acid, absorbed but one-ninth as much as the unaltered 
earth. The treatment with the various lime-salts increas- 
ed the absorbent power, in the order of the Table, until 
in the last instance it surpassed that of the original soil. 
Here, too, we observe that the absorption of potash ac- 
companies and is made possible by the displacement of 
other bases, (in this case almost entirely lime, since the 
treatment with acid had nearly removed the others). We 
observe further that the quantity of chlorine remained 
the same throughout (within the limits of experimental 
error,) not being absorbed in any instance. 

Way first showed that the absorptive power of the soil 



ABSORPTIVE POWER OF THE SOIL. 343 

is diminished or even destroyed by lurning or calcination. 
Peters, experimenting on this point, obtained the follow- 
ing results : 

Potash absorbed from solution of chloride of potassium by 
uuburned burned 

Vegetable mould, 0.2515 0.0303 

Loam, 0.1841 0.1300 

The Cause of the Absorptive Power of Soils for 

Bases when combined with chlorine, sulphuric, and nitric 
acids, has been the subject of several extensive investiga- 
tions. Way, in his papers already referred to, was led to 
conclude that the quality in question belongs to some pe- 
culiar compound or compounds that are associated with 
the clayey or impalpable portion of the soil. That these 
bodies were compounds of the bases of the soil with 
silica, was a most probable and legitimate hypothesis, 
which he at once sought to test by experiment. 

Various natural silicates, feldspars, and others, and some 
artificial preparations, were examined, but found to be 
destitute of action. Finally, a silicate of alumina and 
soda containing water was prepared, which possessed ab- 
sorptive properties. 

To produce this compound, pure alumina was dissolved 
in solution of caustic soda on the one hand, and pure silica 
in the same solution on the other. On mingling the two 
liquids, a white precipitate separated, which, when washed 
from soluble matters and dried at 212°, had the following 
composition * : 

Silica, 46.1 

Alumina, 26.1 

Soda, 15.8 

Water, 12.0 



100.0 



* Way gives the composition of the anhydrous salt, and says it contained, 
dried at 212% about 12 per cent of water. In the above statement this water is in- 
cluded, since it is obviously an essential ingredient. 



344 HOW CKOPS FEED. 

This compound is analogous in constitution to the 
zeolites, in so far as it is a highly basic silicate containing 
water, and is easy of decomposition. It is, in fact, de- 
composed by water alone, which removes from it silicate 
of soda, leaving insoluble silicate of alumina. 

On digesting this soda-silicate of alumina with a solu- 
tion of any salt of lime, Way found that it was decom- 
posed, its soda was eliminated, and a lime-silicate of 
alumina was produced. In several instances he succeeded 
in replacing nearly all the soda by lime. Potash-silicate 
of alumina was procured by acting on either the soda or 
lime silicate with solution of a potash-salt ; and, in a suni- 
lar manner, ammonia and magnesia-silicates were gener- 
ated. In case of the ammonia-compound, however. Way 
succeeded in replacing only about one-third of soda or 
other base by ammonia. All of these compounds, when 
acted upon by pure water, yielded small proportions of 
alkali to the latter, viz. : 

The Boda- silicate gave 3.36 parts of soda to 10,000 of water. 
The potash- " " 2.2T " " potash '' " '• " 
The ammonia- '^ " 1.06 " "ammonia" " " " 

Way found furthermore that exposure to a strong heat 
destroyed the capacity of these substances to undergo the 
displacements we have mentioned. 

From these facts Way, concluded that there exist in all 
cultivable soils, compounds similar to those he thus pro- 
cured artificially, and that it is their presence which oc- 
casions the absorptions and displacements that have been 
noticed. 

Way gives as characteristic of this class of double sili- 
cates, that there is a regular order in which the common 
bases replace each other. He arranges them in the fol- 
lowing series : 

Soda — Potash — Lime — Magnesia — Ammonia: 
and according to him, potash can replace soda but not the 
other bases; while ammonia replaces them all : or each base 



ABSORPTIVE POWER OF THE SOIL. 345 

replaces those ranged to its left in the above series, but 
none of those on its right. Way remarks, that " of course 
the reverse of this action cannot occur." Liebig {Ajin. der 
Chem. u. Pharm.^ xciv, 380) drew attention to the fact 
that Way himself in the preparation of the potash-alumi- 
na-silicate, demonstrated that there is no invariable order 
of decomposition. For, as he asserts, this compound may 
be obtained by digesting either the lime-alumina-silicate, or 
soda-alumina-silicate in nitrate or sulphate of potash, when 
the soda or lime is dissolved out and replaced by potash. 

Way was doubtless led into the mistake of assuming a 
fixed order of replacements by considering these exchanges 
of bases as regulated after the ordinary manifestations of 
chemical affinity. His own ex23eriments show that among 
these silicates there is not only no inflexible order of de- 
composition, but also no complete replacements. 

The researches of Eichhorn, " Ueber die Einwirkung ver- 
diinnter Salzlosungen auf Ackererde," {Landwirthschaft- 
liches Centralhlatt^ 1858, ii, 169, and Pogg. Ann., No. 9, 
1858), served to clear up the discrepancies of Way's in- 
vestigation, and to confirm and explain his facts. 

As Way's artificial silicates contained about 12 per cent 
of water, the happy thought occurred to Eichhorn to test 
the action of saline solutions on the hydrous silicates 
(zeolites) Avhich occur in nature. He accordingly insti- 
tuted some trials on chabazite, an abstract of which is 
here given. 

On digesting finely pulverized chabazite (hydrous sili- 
cate of alumina and lime) with dilute solutions of chlo- 
rides of potassium, sodium, ammonium, lithium, barium, 
strontium, calcium, magnesium, and zinc, sulphate of 
magnesia, carbonates of soda and ammonia, and nitrate 
of cadmium, he found in every case that the basic ele- 
ment of these salts became a part of the silicate, while 
lime passed into the solution. The rapidity of the re- 
placement varied exceedingly. The alkali-chlorides re- 
15* 



346 HOW CROPS FEED. 

acted evidently in two or three days. Chloride of barium 
and nitrate of cadmium were slower in their effect. Chlo- 
rides of zinc and strontium at first, appeared not to react ; 
but after twelve days, lime was found in the solution. 
Chloride of magnesium was still tardier in replacing lime. 
Four grams of powdered chabazite were digested with 
4 grams of chloride of sodium and 400 cubic centimeters 
of water for 10 days. The composition of the original.; 
mineral (i,) and of the same after the action of chloride of 
sodium (ii,) were as follows : 





I. 


II. 


Silica, 


47.44 


48.31 


Alumina, 


20.69 


21.04 


Lime, 


10.37 


6.65 


Potash, 


0.65 


0.64 


Soda, 


0.43 


5.40 


Water, 


20.18 


18.33 



Total, 99.75 100.37 

Nearly one-half the lime of the original mineral was 
thus substituted by soda. A loss of water also occurred. 
The solution separated from the mineral, contained nothing 
but soda, lime, and chlorine, and the latter in precisely its 
original quantity. 

By acting on chabazite with dilute chloride of ammo- 
nium (10 grams to 500 c.c. of water) for 10 days, the 
mineral was altered, and contained 3.33 per cent of am- 
monia. Digested 21 days, the mineral yielded 6.94 per 
cent of ammonia, and also lost water. 

These ammonia-chabazites lost no ammonia at 212°, it 
escaped only when the heat was raised so high that water 
began to be expelled ; treated with warm solution of pot- 
ash it was immediately evolved. The ammonia-silicate 
was slightly soluble in water. 

As in the instances above cited, there occurred but a 
partial displacement of lime. Eichhorn made correspond- 
ing trials with solutions of carbonates of soda and am- 



ABSORPTIVE POWER OF THE SOIL. 347 

monia, in order to ascertain whether the formation of a 
soluble salt of the displaced base limited the reaction ; 
but the results were substantially the same as before, as 
shown by analyzing the residue after removing carbonate 
of lime by digestion in dilute acetic acid. 

Eichhorn found that the artificial soda-chabazite re-ex- 
changed soda for lime when digested in a solution of 
chloride of calcium ; in solution of chloride of potassium, 
both soda and lime were separated from it and replaced 
by potash. So, the ammonia-chabazite in solution of chlo- 
ride of calcium, exchanged ammonia for lime, and in so- 
lutions of chlorides of potassium and sodium, both am- 
monia and lime passed into the liquid. The ammonia- 
chabazite in solution of sulphate of magnesia, lost ammo- 
nia but not lime, though doubtless the latter base would 
have been found in the liquid had the digestion been con- 
tinued longer. 

It thus appears that in the case of chabazite all the 
protoxide bases may mutually replace each other, time 
being the only element of difference in the reactions. 

Similar observations were made with natrolite (hydrous 
silicate of alumina and soda,) as well as with chlorite and 
labradorite, although in case of the latter difficultly de- 
composable silicates, the action of saline solutions was 
very slow and incomplete. 

Mulder has obtained similar displacements with the 
zeolitic minerals stilbite, thomsonite, and prehnite. ( Che- 
mle der AckerJcrume, I, 396). He has also artificially 
prepared hydrous silicates, having properties like those 
of Way, and has noticed that sesquioxide of iron readily 
participates in the dis]3lacements. Mulder also found that 
the gelatinous zeoUtic precipitate obtained by dissolving 
hydraulic cement in hydrochloric acid, precipitating by 
ammonia and long washing with water, underwent^ the 
same substitutions when acted upon by saline solutions. 



348 HOW CHOPS FEED. 

The precipitate he operated with, contained (water-free) 
in 100 parts : 

Silica 49.0 

Alumina 11.1 

Oxide of iron 21.9 

Lime 6.9 

Magnesia 1.1 

Insoluble matters -with traces of alkalies, etc 10.0 

100.0 
On digesting portions of this substance with solutions 
of sulphates of soda, potash, magnesia, ammonia, for a 
single hour, all the lime was displaced and replaced by- 
potash — two-thirds of it by soda and nearly four-fifths of 
it by magnesia and ammonia. 

Further investigations by Rautenberg {Henneberg' s 
Jour, fur Jjandiolrthschaft, 1862, pp. 405-454), and 
Knop ( Vs. St.^ YII, 57), which we have not space to re- 
count fully, have demonstrated that of the bodies possible 
to exist in the soil, those in the following list do not pos- 
sess the power of decomposing sulphates and nitrates of 
lime, potash, ammonia, etc., viz.: 

hD C Quartz sand. "] 

o3 Kaolinite (purified kaolin.) | 
'^ Carbonate of lime (chalk.) 'These bodies have no absorptive effect, either 

Humus (decayed wood.) f separately or together. 

Hydratcd oxide of iron. | "1 

^Hydrated alumina, J 

Humate of lime, magnesia, and alumina. I Knop. 

Phosphate of alumina. j 

Gelatinous silica. 

" " dried in the air. J 

These observers, together with 'H.Qidien {Jahreshericht 
ilher Agriculturchemie^ 1864, p. 17), made experiments on 
soils to which hydrated silicates of alumina, and soda, or 
of lime, etc., were added, and found their absorptive 
power thereby increased. 

Kautenberg and Heiden also found an obvious relation 
to subsist between the absorjjtive powers of a soil and cer- 
tain of its ingredients. Rautenberg observed that the ab- 
sorptive power of the nine soils he operated with was 
closely connected with the quantity of alumina and ox- 



ABSORPTIVE POWEli OF THE SOIL. 349 

ide of iron which the soils yielded to hydrochloric acid. 
Heiden traced a similar relation between the silica set free 
by the action of acids on eleven soils and their absorptive 
power. Rautenberg and Heiden further confirmed what 
Way and Peters had previously shown, viz., that treat- 
ment of soil with acids diminished their absorbent power. 
These facts admit of interpretation as follows : Since 
neither silica, hydrated alumina, nor hydrated oxide of 
iron, as such, have any absorptive or decomposing power 
on sulphates, nitrates, etc., and since these bodies do not 
ordinarily exist as such to much extent in soils, therefore 
the connection found in twenty cases to subsist between 
their amount (soluble in acids) in the soil, and the ab- 
sorptive power of the latter points to a compound of 
these (and other) substances (silicate of alumina, iron, 
lime, etc.), as the absorptive agent. 

That the absorbing compound is not necessarily hydra- 
ted, is indicated by the fact that calcination, which must 
remove water, though it diminishes, does not always alto- 
gether destroy the absorptive quality of a soil. (See p. 
343.) Eichhorn, as already stated, found that the anhy- 
drous silicates, chlorite and labradorite, were acted upon 
by saline solutions, though but slowly. 

Do Zeolitic Silicates, hydrated or otherwise, exist 
in the Soil ] — When a soil which is free from carbonates 
and salts readily soluble in water, is treated with 
acetic, hydrochloric, or nitric acid, there is taken up a 
quantity (several per cent.) of matter which, while con- 
taining all the elements of the soil, consists chiefly of 
alumina and oxide of iron. Silica is not dissolved to much 
extent in the acid, but the soil which before treatment 
with acid contains but a minute amount of uncombined 
silica, afterwards yields to the proper solvent (hot solution 
of carbonate of soda) a considerable quantity. This is our 
best evidence of the presence in the soil of easily decom- 



350 



HOW CROPS TEED. 



posable silicates. A number of analyses which illustrate 
these facts are subjoined : 



Water 

Organic matter 

Sand and insoluble Bilicates. 

(Clay, kaolinite) 

f Silica 

Oxide of iron 

Alumina 

Lime 

Magnesia 

Potash 

Soda 

Phosphoric acid 

Sulphuric acid 

Carbonic acid, chlorine, 

. and loss 



Sandy Loam. 
Heiden. 



1.613 
2.387 
89.754 
(10.344) 
2.630* 
1.872 
1.152 
0.101 
0.201 
0.242 
0.034 
0.083 
0.007 

0.047 



1.347 

2.003 

88.782 

^5.762) 

"4.199 

1.630 

1.283 

0.122 

0.240 

0.212 

0.141 

0.034 

0.021 

0.095 



100.000 100.000 100.00 



White 
Clay. 



5. 

Porce- 
lain 
Clay. 

Rautenberg. 



Red 
Clay. 



6.15 
none 
58.03 

18.73 
2.11 

12.15 
0.27 
0.29 
0.86 
1.41 

none 



6.39 
none 
80.51 



0.90 
4.35 
0.38 
0.17 



0.50 



100.00 



10.36 
none 
89.46 

0.04t 
j-0.14 

0.12 
0.08 



100.20 



White 

Pottery 

Clay. 

Wat. 



6.18 
none 

58.72 

13.41 
5.38 

13.90 
0.61 
0.43 



1.37 



100.00 



* This soil yielded to solution of carbonate of soda before treatment with 
acid, 0.340 o|o silica. 
t The silica in this case is the small portion held in the acid solution. 

The first three analyses especially, show that the soils 
to which they refer, contained a silicate or silicates in 
which iron, alumina, lime, magnesia and the alkalies ex- 
isted as bases. How much of such silicates may occur in 
any given soil is impossible to decide in the present state 
of our knowledge. In the soil, free silica, is usually, if not 
always present, as may be shown by treatment with solu- 
tion of carbonate of soda, but it appears difficult, if not 
impossible, to ascertain its quantity. Again, hydrated 
oxide of iron (according to A. Miiller and Knop) and hy- 
drated alumina'^ (Knop) may also exist, as can be made 
evident by digesting the soil in solution of tartrate of 
soda and potash (Miiller, Vs. jSt, IV, p. 277), or in a mix- 
ture of tartrate and oxalate of ammonia (Knop, Vs. St. 
VIII, p. 41). Finally, organic acids occur to some ex- 
tent in insoluble combinations with iron alumina, lime. 



• More probably, highly basic carbonates, or mixtures of hydrates and car- 
bonates. 



ABSORPTIVE POWER OF THE SOIL. 351 

&c. This complexity of the soil effectually prevents an 
accurate analysis of its zeolitic silicates. 

If further evidence of the existence of zeolitic com- 
pounds in the soil were needful, it is to be found in con- 
sidering the analogy of the conditions which there obtain 
with those under which these compounds are positively 
known to be formed. 

At Plombieres, in France, the water of a hot spring 
(temperature, 140^^ F.) ' has flowed over and penetrated 
through a mass of concrete, composed of bricks and sand- 
stone laid in lime, which was constructed centuries ago by 
the Romans. The water contains about nine ten-thou- 
sandths of solid matter in solution, a quantity so small as 
not to affect its taste perceptibly. As Daubree has shown 
{Ann. des Mi7ies^ 5me., Serie, T. XIII, p. 242), the cavi- 
ties in the masonry frequently exhibit minute but well- 
defined crystals of various zeolitic minerals, viz. : chaba- 
site, apoj^hyllite, scolezite, harmotome, together with hy- 
drated silicate of lime. These minerals have been pro- 
duced by the action of the water upon the bricks and lime 
of the concrete, and while a high temperature prevails 
there, which probably has facilitated the crystallization of 
the minerals, as it certainly has done the chemical altera- 
tion of the bricks and sandstone, the conditions otherwise 
are just those of the soil. 

In the soil, we should not expect to find zeolitic com- 
binations crystallized or recognizable to the eye, because the 
small quantities of these substances that could be formed 
there must be distributed throughout twenty, fifty, or 
more times their weight of bulky matter, which would 
mechanically prevent their crystallization or segregation 
in any form, more especially as the access of water is very 
abundant ; and the carbonic acid of the surface soil, which 
powerfully decomposes silicates, would operate antago- 
nistically to their accumulation. 



352 HOW CROPS FEED. 

The water of the soil holds silica, lime, magnesia, alka- 
lies, and oxide of iron, often alumina, in solution. In- 
stances are numerous in which tlie evaporation of water 
containing dissolved salts has left a solid residue of sili- 
cates. Thus, Kersten has described {Jour, filr praJct. 
Chem., 22, 1) a hydrous silicate of iron and manganese 
that occurred as a hard incrustation upon the rock, in one 
of the Freiberg mines, and was deposited where the water 
leaked from the pumps. Kersten and Berzelius have no- 
ticed in the evaporation of mineral waters which contain 
carbonates of lime and magnesia, together with silica, that 
carbonates of these bases are first deposited, and finally 
silicates separate. {Bischofs Chem. Geology^ Cav. JEd., 
Vol. 1, p. 5). Bischof {loc. cit.^ p, 6) has found that silica, 
even in its most inactive form of quartz, slowly decom- 
poses carbonate of soda and potash, forming silicate when 
boiled with their aqueous solutions. Undoubtedly, simple 
contact at ordinary temperature has the same eifect, 
though more slowly and to a slight extent. 

Such facts make evident that silica, lime, the alkalies, 
oxide of iron and alumina, when dissolved in water, if they 
do not already exist in combination in the water, easily 
combine when adverse affinities do not prevent, and may 
react upon the ingredients of the soil, or upon rock dust, 
with the formation of zeolites. 

The "pan," w^hich often forms an impervious stratum 
under peat bogs, though consisting largely of oxide of iron 
combined with organic acids, likewise contains consider- 
able quantities of hydrated silicates, as shown by the 
analyses of Warnas and Michielsen (Mulder^s Chem. d. 
Ackerkrumey Bd. 1, p. 566.) 

Mulder found that when Portland cement (silicate of 
lime, alumina, iron, etc.) was treated with strong hydro- 
chloric acid, whereby it was decomposed and in part dis- 
solved, and then with ammonia, (which neutralized and re- 



ABSORPTIVE POWER OF THE SOIL. 853 

moved the acid,) the gelatinous precipitate, consisting 
chiefly of free siUca, free oxide of iron, free aUimina, with 
smaller quantities of lime and magnesia, contained never- 
theless a portion of silica, and of these bases in combina- 
tion, because it exhibited absorbent power for bases, like 
Way's artificial silicates and like ordinary soil. Mere 
contact of soluble silica or silicates, with finely divided 
bases, for a short time^ is thus proved to be sufiicient for 
chemical union to take place between them. 

iJlecently precipitated silicic acid being added to lime- 
water, unites with and almost completely removes the lime 
from solution. The small portion of lime that remains 
in the liquid is combined with silica, the silicate not being 
entirely insoluble. (Gadolin, cited in Stover's Diet, of 
/Solubilities^ p. 551.) 

The fact that free bases, as ammonia, potash and lime, 
are absorbed by and fixed in soils or clays that contain no 
organic acids, and to a degree different, usually greater than, 
when presented in combination, would indicate that they 
directly unite either with free silica or with simple sili- 
cates. The hydrated oxide of iron and alumina are in- 
deed, under certain conditions, capable of retaining free 
alkalies, but only in minute quantities. (See p. 359.) 

The fact that an admixture of carbonate of lime, or of 
other lime-salts with the soil, usually enhances its absorbent 
power, is not improbably due, as Rautenberg first suggest- 
ed, to the formation of silicates. 

A multitude of additional considerations from the his- 
tory of silicates, especially from the chemistry of hydraulic 
cements and from geological metamorphism, might be 
adduced, were it needful to fortify our position. 

Enough has been written, however, to make evident 
that silica, which is, so to speak, an accident in the plant, 
being unessential (we will not affirm useless) as one of its 
ingredients, is on account of its extraordinary capacity for 
chemical union with other bodies in a great variety of 



354 HOW CROPS FEED. 

proportions, extremely important to the soil, and espe- 
cially so when existing in combinations admitting of the 
remarkable changes which have come under our notice. 

That we cannot decide as to the precise composition of 
the zeolitic compounds which may exist in the soil, is plain 
from what has been stated. We have the certainty of 
their analogy with the well-defined silicates of the miner- 
alogist, which have been termed zeolites, an analogy of 
chemical composition and of chemical j^roperties ; we know 
further that they are likely to be numerous and to be in 
perpetual alteration, as they are subjected to the influence 
of one and another of the salts and substances that are 
brought into contact with them ; but more than this, at 
present, we cannot be certain of. 

Physical agencies in the phenomena of absorption. — 

While the absorption by the soil of potash or other base 
is accompanied by a chemical decomposition, which Way, 
Rautenberg, Heiden, and Knop's researches conclusively 
connect with certain hydrous silicates whose j^resence in 
the soil cannot be doubted, it has been the opinion of 
Liebig, Brustlein, Henneberg, Stohmann and Peters, 
that the real cause of the absorption is physical, and is 
due to simple surface attraction (adhesion) of the porous 
soil to the absorbed substance. Brustlein and Peters have 
shown that bone and wood-charcoal, washed with acids, 
absorb ammonia and potash from their salts to some ex- 
tent, and after impregnation with carbonate of lime to as 
great an extent as ordinary soil. While the reasons al- 
ready given appear to show satisfactorily that the ab- 
sorbent power of the soil, for bases in combination^ re- 
sides in the chemical action of zeolitic silicates, the facts 
just mentioned indicate that the physical properties of the 
soil may also exert an influence. Indeed, the fixation of 
free bases by the soil may be in all cases partially due to 
this cause, as Brustlein has made evident in case of am- 
monia {BoussingauWs Agronomie, etc., T., II, p. 153). 



ABSORPTIVE POWER OF THE SOIL. 355 

Peters concludes the account of bis valuable investiga- 
tion with the following words: ^'-Absorption is caused by 
the surface attraction wJiich the particles of earth exert. 
In the absorption of bases from salts, a chemical trans- 
position with the ingredients of the soil is necessary, 
which is m^ade possible through cooperation of the surface 
attraction of the soil for the base^ (Vs. St., II, p. 151.) 

If we admit the soundness of this conclusion, we must 
also admit that in the soil the physical action is exerted 
in sufficient intensity to decompose salts, by the hydrated 
silicates cdone. We must also allow that the displace- 
ments observed by Way and Eichhorn in silicates, are 
primarily due to mere physical action, though they have 
undeniably a chiefly chemical aspect. 

That the phenomena are modified and limited in certain 
respects by physical conditions, is to be expected. The 
facts that the quantity of solution compared with the 
amount of soil, the strength of the solution, and up to 
a certain point the time of contact, influence the degree 
of absorption, point unmistakably to purely physical in- 
fluences, analogous to those with whose action the chem- 
ist is familiar in his daily experience. 

Absorption of Acids* — It has been mentioned 
already that phosphoric and silicic acids are absorbed 
by soils. Absorption of phosphoric acid has been 
invariably observed. In case of silicic acid, excep- 
tions to the rule have been noticed. In very few in- 
stances has the absorption of sulphuric and nitric acids 
or chlorine, from their compounds, been remarked 
hitherto by those who have investigated, the ab- 
sorbent power of the soil. The nearly universal con- 
clusion has been that these substances are not subject in 
any way, chemical or physical, to the attraction of the 
soil. Yoelcker was the first to notice an absorption of 
sulphuric acid and chlorine. In his papers on "Farm 
Yard Manure," etc., (Jour. Roy. Ag. Soc, XVIII., p. 140,) 



356 HOW CROPS FEED. 

and on the " Changes which Liquid Manure undergoes in 
contact with different Soils of Known Composition" (idem 
XX., 134-57), he found, in seven experiments, that dung 
liquor, after contact with various soils, lost or gained acid 
ingredients, as exhibited by the following figures, in grains 
per gallon : (loss is indicated by — , gain by +) : 

1 2 345 67 A. B.- 

Chloride of Potassium —8.81 +9.17 — 2.74 +2.14 —2.74 +2.55 —1.10 

Chloride of Sodium. . .—3.95 —2.43 —7.04 —1.12 —1.10 —1.24 +3.60 —1.89 +19.05 

Sulphuric Acid +3.32 -4.21 — l.Og —1.21 —0.27 +1.24 +3.44 +2.20 —9.42 

Silicic Acid +1.63 +10.33 —1.04 +0.72 +2.76 —0.11 —0.07 undet. —1.57 

Phosphoric Acid — — —4.23 —3.09 —2.91 —3.38 —0.13 —8.76 —7.71 

"We notice that chlorine was perceptibly retained in 
three instances, while in the other four it was, on the 
whole, dissolved from the soil. Sulphuric acid was re- 
moved from the solution in four instances, and taken up 
by it in three others. In four cases silica was absorbed, 
and in three was dissolved. In his first paper. Professor 
Way recorded similar experiments, one with flax-steep 
liquor and a second with sewage. The results, as regards 
acid ingredients, are included in the above table, A and B, 
where we see that in one case a slight absorption of chlo- 
rine, and in the other of sulphuric acid, occurred. Way, 
however, regards these differences as due to the unavoid- 
able errors of experiment, and it is certain that in Voelck- 
er's results similar allowance must be made. ISTeverthe- 
less, these errors can hardly account for the large loss of 
chlorine observed in 1 and 3, or of sulphuric acid in 2. 

Liebig found in his experiments "that a clay or lime- 
soil, poor in organic matter, withdrew from solution of 
silicate of potash, both silicic acid and potash, whereas 
one rich in humus extracted the potash, but left the silicic 
acid in solution." (Compare pp. 171-5.) 

As regards nitric acid ^ Knop observed in a single in- 
stance that this body could not be wholly removed by 
water from a soil to which it had been added in known 
quantity. He regards it probable that it was actually 



ABSORPTIVE POWER OF THE SOIL. 357 

retained rather than altered to ammonia or some other 
compound. 

The fixation of acids in the soil is unquestionably, for 
the most part, a chemical process, and is due to the for- 
mation of comparatively insoluble compounds. 

Hydrated oxide of iron and hydrated alumina are 
capable of forming highly insoluble compounds with all 
the mineral acids of the soil. The chemist has long been 
familiar with basic chlorides, nitrates, sulphates, silicates, 
phosphates and carbonates of these oxides. Whether such 
compounds can be actually produced in the soil is, how- 
ever, to some extent, an open question, especially as re- 
gards chlorine, nitric and sulphuric acids. Their forma- 
tion must also greatly depend upon what other substances 
are present. Thus, a soil rich in these hydrated oxides, 
and containing lime and the other bases in minuter quan- 
tity (except as firmly combined in form of silicates,) would 
not unlikely fix free nitric acid or free sulphuric acid as 
well as the chlorine of free hydrochloric acid. "When the 
acids are presented in the form of salts, however, as is 
usually the case, the oxides in question have no power to 
disi^lace them from these combinations. The acids, can- 
not, therefore, be converted into basic aluminous or iron 
salts unless they are first set free — unless the bases to 
which they were previously combined are first mastered 
by some separate agent. In the instance before referred 
to where nitric acid disappeared from a soil, Knop sup- 
poses that a basic nitrate of iron may have been formed, 
the soil employed being, in fact, highly ferruginous. 
The hydrated oxides of iron and alumina do, however, 
form insoluble compounds with phosphoric acid^ and may 
even remove this acid from its soluble combinations with 
lime, as Thenard has shown, or even, perhaps, from its 
compounds with alkalies. 

Phosphoric acid is fixed by the soil in various ways. 
When a phosphate of potash, for example, is put in 



358 HOW CROPS FEED. 

contact with the soil, the base may be withdrawn by the 
absorbent silicate, and the acid may unite to lime or mag- 
nesia. The phosphates of lime and magnesia thus formed 
are, however, insoluble, and hence the acid as well as the 
base remains fixed. Again, if the alkali-phosphate be 
present in quantity so great that its base cannot all be 
taken up by the absorbent silicate, then the hydrated 
oxide of iron or alumina may react on the phosphate, chemi- 
cally combining with the pliosphoric acid, while the alkali 
gradually saturates itself with carbonic acid from the air. 
It is, however, more likely that organic salts of iron (cre- 
nates and apocrenates) transpose with the phosphate. So, 
too, carbonate of lime may decompose with phosphate of 
potash, producing carbonate of potash and phosphate of 
lime (J. Lawrence Smith). Ycelcker, in a number of ex- 
periments on the deportment of the soluble superphosphate 
of lime toward various soils, found that the absorption of 
phosphoric acid was more rapid and complete with soils 
containing much carbonate of lime than with clays or 
sands. 

All observers agree that phosphoric acid is but slowly 
fixed by the soil. Voelcker found the process was not 
completed in 26 days. Its absorption is, therefore, mani- 
festly due to a difierent cause from that which completes 
the fixation of ammonia and potash in 48 hours. 

As to silicic acid^ it may also, as solid hydrate, unite 
slowly with the oxides of iron and with alumina (see Kers- 
ten's observations, p. 352). When occurring in solution, as 
silicate of an alkali, as happens in dung liquor, it would 
be fixed by contact with solid carbonate of lime, silicate 
of lime being formed (Fuchs, Kuhlmann), or by encoun- 
tering an excess of solutions of any salt of lime, magnesia, 
iron or ammonia. In presence of free carbonic acid in 
excess, a carbonate of the alkali would be formed, and the 
silicic acid would be separated as such in a nearly insoluble 



ABSOEPTIVE POWEE OF THE SOIL. 359 

form. Dung liquor, rich in carbonate of potash, on the 
other hand, would dissolve silica from the soil. 

Sulphuric acid, existing in considerable quantities in 
dung liquor as a readily soluble salt of ammonia or potash, 
would be partially retained by a soil rich in carbonate of 
lime by conversion into sulphate of lime, which is com- 
paratively insoluble. 

Absorption of Bases, from their Hydrates, Carbonates 
and Silicates* — 1. Incidentally it has been remarked that 
free bases, among which ammonia, potash, soda and lime 
are specially implied, may be retained by combining with 
undissolved silica. Potash, soda (and ammonia?) may 
at once form insoluble compounds if the silica be in large 
proportion ; otherwise they may produce soluble silicates, 
wliich, however, in contact with lime, magnesia, alumina 
or iron salts, will yield insoluble combinations. As is 
well proved, gelatinous silica and lime at once form a 
nearly insoluble compound. It is probable that gelatinous 
silica may remove magnesia from solution of its bicarbon- 
ate, forming a nearly insoluble silicate of magnesia. 

2. It has long been known that hydrated oxide of iron 
and hydrated alumina may unite with and retain free 
ammonia, potash, etc. Rautenberg experimented with 
both these substances as freshly prepared by artificial 
means, and found that, under similar conditions, 

10 grms. of hydrated 10 grms. of hydrated 
oxide of iron. alumina. 

Absorbed of free ammonia 0.046 grm. 0.066 grm. 

" " free potash - 0.147 " not det. 

Long continued washing with water removes the alkali 
from these combinations. That oxide of iron and alumina 
commonly occur in the soil in quantity sufficient to have 
appreciable effect in absorbing free alkalies is extremely 
improbable. 

Liebig has shown {Ann. Ch. u. Ph. 105, p. 122,) that 
hydrated alumina unites with silicate of potash with great 



360 HOW CROPS FEED. 

avidity (an insoluble double silicate being formed just as 
in the experiments of Way, p. 343). According to Liebig, 
a quantity of hydrated alumina equivalent to 2.696 grms. 
of anhydrous alumina, absorbed from a liter of solution 
of silicate of potash containing 1.185 grm. of potash and 
3.000 grm. of silica, fifteen per cent of the silicate. Doubt- 
less hydrated oxide of iron would behave in a similar 
manner. 

3. The organic acids of humus are usually the most 
effective agents in retaining the bases when the latter are 
in the free state, or exist as soluble carbonates or silic- 
ates. The i^roperties of the humates have been detailed 
on page 230. It may be repeated here that they form 
with the alkalies''' when the latter jDreponderate, soluble 
salts, but that these compounds unite readily to other 
earthy* and metallic* humates, forming insoluble com- 
pounds. Lime at once forms an insoluble humate, as 
do the metallic oxides. When, as naturally happens, the 
organic acids are in excess, their effect is in all cases to 
render the soluble free bases or their carbonates nearly 
insoluble. 

In some cases, ammonia, potash and soda are absorbed 
more largely from their carbonates than from their hy- 
drates. Thus, in some experiments made by the author, 
a sample of Peat from the N'ew Haven Beaver Meadow 
was digested with diluted solution of ammonia for 48 
hours, and then the excess of ammonia was distilled off 
at a boiling heat. The peat retained 0.95" \^ of this alkali. 
Another portion of the same peat was moistened with 
diluted solution of carbonate of ammonia and then dried 
at 212° until no ammoniacal smell was perceptible. This 
sample was found to have retained 1.30° \^ of ammonia. 
This difference was doubtless due to the fact that the 



* In the customary language of Chemistry, potash, soda, and ammonia are 
alkalies or alkali-bases. Lime, magnesia, and alumina are earths or earthy bases, 
and oxide of iron and oxide of manganese are metallic bases. 



REVIEW AND CONCLUSION. 361 

peat contained humate q/*^*/??e, which was not affected by 
the pure ammonia, but in contact with carbonate of am- 
monia yielded carbonate of hme and humate of ammonia. 
In these cases the ammonia was in excess^ and the chemical 
changes were therefore, in some particulars, unlike those 
which occur when the humus preponderates. 

Brustlein, Liebig and others have observed that soils 
rich in organic matter (forest mold, decayed wood,) have 
their absorptive power much enhanced by mixture with 
carbonate of lime. 

Although Rautenberg has shown {Menneherg's Journal 
186, p. 439,) that silicate of lime is probably formed when 
ordinary soils are mixed with carbonate of lime, it may 
easily happen, in the case of soils containing humus, that 
humate of lime is produced, which subsequently reacts 
upon the alkali-hydrates or salts with which absorption 
experiments are usually made. 



§ 6. 
KEVIEW AND CONCLUSION. 

The limits assigned to this work having been nearly 
reached, and the more important facts belonging to the 
present chapter brought under notice, with considerable 
fulness, it remains to sum up and also to adduce a few 
considerations which may appropriately close the volume. 
There are indeed a number of topics connected with the 
feeding of crops which have not been treated uj^on, such, 
especially as come up in agricultural practice ; but these 
find their place most naturally and properly in a discussion 
of the improvement of the soil by tillage and fertilizers, 
to which it is proposed to devote a third volume. 

What the Soil must contain* — In order to feed crops, 
16 



362 



HOW CKOPS FEED. 



the soil must contain the ash-ingredients of plants, together 
with assimilable nitrogen-compounds in proper quantity 
and proportion. The composition of a very fertile soil is 
"Well exhibited by Baumhauer's analysis of an alluvial de- 
posit from the waters of the Rhine, near the Zuider Zee, 
in Holland, This soil, which produces large crops, con- 
tained — 





Surface. 


15 incites deep. 


30 inches d 


Insoluble silica, quartz, 


57.646 


51.706 


55.372 


Soluble silica, 


s.aio 


2.496 


2.286 


Alumina, 


1.830 


2.900 


2.8SS 


Peroxide of iron. 


9.039 


10.305 


11.864 


Protoxide of iron, 


0.350 


0.563 


0.200 


Oxide of manganese. 


0.288 


0.354 


0.284 


Lime, 


4.092 


5.096 


2.480 


Magnesia, 


0.130 


0.140 


0.128 


Potash, 


1.026 


1.430 


1.521 


Soda, 


1.9T2 


2.069 


1.937 


Ammonia,* 


0.060 


0.078 


0.075 


Phosphoric acid, 


0.466 


0.324 


0.478 


Sulphuric acid, 


0.896 


1.104 


0.576 


Carbonic acid. 


6.085 


6.940 


4.775 


Chlorine, 


1.240 


1.302 


1.418 


Humic acid. 


2.798 


3.991 


3.428 


Crenic acid, 


0.771 


0.731 


0.037 


Apocrenic acid. 


0.107 


0.160 


0.152 


Other organic matters, and com- 








bined water (nitrates ?), 


8.324 


7.700 


9.348 


Lobs in analysis. 


0.540 


0.611 


0.753 



lOO.QOO 



100.000 



100.000 



A glance at the above analyses shows the unusual rich- 
ness of this soil in all the elements of plant-food, with ex- 
ception of nitrates, which were not separately determined. 
The alkalies, phosphoric acid, and sulphuric acid, were 
present in large proportion. The absolute quantities of 
the most important substances existing in an acre of this 
soil taken to the depth of one foot, and assuming this 



* The figures are probably too high for ammonia, because, at the time the analy- 
ses were made, the methods of estimating this substance in the soil had not been 
etudied suflSciently, and the ammonia obtained was doubtless derived in great 
part from the decomposition of humus under the action of an alkali. 



REVIEW AND CONCLUSION. 



363 



quantity to weigh 3,500.000 lbs., (p. 158,) are as follows; 





lbs. 


Soluble silica 


81.900 


Lime, 


143.220 


Potash, 


35.910 


Soda, 


68,920 


Ammonia, 


2.100 


Phosphoric acid, 


16.310 


Sulphuric acid, 


31.360 


Nitric acid, 


? 



Quantity of Available Ash-ingredients necessary for 

a Maximum Crop. — ^We have already given some of the 
results of Hellriegel's experiments, made for the purpose 
of determining how much of the various elements of nu- 
trition are required to produce a maximum yield of cereals 
(pp. 215 and 288). This experimenter found that 74 lbs. 
of nitrogen (in form of nitrates) to 1,000.000 of soil was 
sufficient to feed the heaviest growth of wheat. Of his 
experiments on the ash-ingredients of crops, only those 
relating to potash have been published. They are here 
reproduced. 

EFFECTS OF VARIOUS PROPORTIONS OF AVAILABLE POTASH • E^ 
THE SOIL ON THE BARLEY CROP. 



Potash in 
l,(m.OOOlbs.oftoU. 




Yield 




of Straw and Chaff. 


of Grain. 


Total. 





0.798 










6 


3.869 


2.993 


6.802 


12 


5.740 


4.695 


10.435 


24 


6.859 


7.851 


14.710 


47 


8.195 


9.578 


17.773 


71 


9.327 


10.097 


19.424 


94 


8. 693 


9.083 


17.776 


141 


8.764 


8.529 


17.293 


282 


8.916 


8.962 


17.878 . 



It is seen that the greatest crop was obtained when 71 
parts of potash were present in 1,000.000 lbs. of soil. A 



* other conditions were in all respects as nearly alilje as possible* 



364 HOW CROPS FEED. 






larger quantity depressed the yield. It is probable that less 
than 71 lbs. would have produced an equal eflfect, since 47 
lbs. gave so nearly the same result. The ash composition 
of barley, grain, and straw, in 100 parts, is as follows, 
according to Zoeller, (H. C. G., pp. 150 to 151) ; 





Grain. 


Straw. 


Potash, 


18.5 


12.0 


Soda, 


3.9 


4.6 


Magnesia, 


7.0 


3.0 


Lime, 


2.7 


7.3 


Oxide of iron, 


0.7 


1.9 


Phosphoric acid, 


32.4 


6.0 


Sulphuric acid. 


2.8 


2.8 


Silica, 


31.1 


59.7 


Chlorine, 


1.1 


2.6 



The proportion of ash in the air-dry grain is 2|- per 
cent, that in the straw is 5 per cent, {Ann. Ch. u. Ph.^ 
CXII, p. 40). Assuming the average barley crop to be 
33 bushels of grain at 53 lbs. per bushel = 1,750 lbs., and 
one ton of straw,* we have in the barley crop of an acre 
the following quantities of ash-ingredients : 

^•^ . I b I -H 1 



^ I -§ « s •!§ J^' #:« ^ 
•§ ^ ^ I s ^1 ^1 ^i ^ 



Barley Grain, 43.75 8.1 1.7 3.1 1.2 0.3 14.2 1.2 0.5 
Straw, 100.00 12.0 4.6 3.0 7.3 1.9 G.O 2.8 2.6 



Total, 143.75 20.1 6.3 6.1 8.5 2.2 20.4 4.0 3.1 

In the account of Hellriegel's experiments, it is stated 
that the maximum barley crop in some other of his trials, 
corresponds to 8,160 lbs. of grain, or 154 bushels of 53 
lbs, each per acre. This is more than 4| times the yield 
above assumed. 

The above figures show that no essential ash-ingredi- 
ent of the oat crop is present in larger quantity than 
potash. Phosphoric acid is quite the same in amount, 

* These figures are employed by Anderson, and are based on Scotch statistics. 



ItEVIEW AND CONCLITSIOX. 365 

while lime is but one-half as much, and the other acids 
and bases are still less abundant. It follows then that if 
71 lbs. of available potash in 1,000.000 of soil are enough 
for a barley crop 4^ times greater than can ordinarily be 
produced under agricultural conditions, the same quantity 
of phosphoric acid, and less than half that amount of lime, 
etc., must be ample. Calculating on this basis, we give 
in the following statement the quantities required per 
acre, taken to the depth of one foot, to produce the max- 
imum crop of Hellriegel (1), and the quantities needed 
for the average crop of 33 bushels (2). The amounts of 
nitrogen are those which Hellriegel found adequate to the 
wheat crop. See p. 289, 







1 


9 






lbs. 


lbs. 


Potash, 




248 


55 


Soda, 




78 


17 


Magnesia, 




76 


17 


Lime, 




105 


23 


Pliosphoric acid, 


250 


55 


Sulplmric 


acid, 


49 


11 


Chlorine, 




38 


8 


Nitrogen, 




245 


54 



If now we divide the total quantities of potash, etc., 
found in an acre, or 3,500.000 lbs. of the soil analyzed by 
Baumhauer, by the number of pounds thus estimated to 
be necessarily present in order to produce a maximum 
or an average yield, we have the following quotients, which 
give the number of maximum barley crops and the number 
of average crops, for which the soil can furnish the re- 
spective materials. 

The Zuidcr Zee soil contains enough 
T iine for 1364 maximum and 6138 average barley crops. 

Potash " lil " " ^8 " " ;' 

Phosphoric acid t>o '^•'~' 

Sulphuric " « 64 " ' 388 

Nitrogen in ammonia "7 ^^ 

We give next the composition of one of the excellent 



366 HOW CROPS FEED. 

wheat soils of Mid Lothian, analyzed by Df. Anderson. 
The air-dry surface-soil contained in 100 parts : 

Silica 71.553 

Alumina.. 6.935 

Peroxide of iron 5.173 

Lime 1.229 

Magnesia 1.083 

Potash 0.354 

Soda 0.433 

Sulpburic acid 0.044 

Phosphoric acid 0.430 

Chlorine traces 

Organic matter 10.198 

Water 3.684 

100.116 

We observe that lime, potash, and sulphuric acid, are 
much less abundant than in the soil from the Zuider Zee. 
The quantity of phosphoric acid is about the same. The 
amount of sulphuric acid is but one-twentieth that in the 
Holland soil, and is accordingly enough for 15 good bar- 
ley crops. 

Lastly may be instanced the author's analysis of a soil 
from the Upper Palatinate, which was characterized by 
Dr. Sendtner, who collected it, as " the most sterile soil in 
Bavaria." 

"Water. 0.535 

Organic matter 1.850 

Silica 0.016 

Oxide of iron and alumina 1.640 

Lime 0.096 

Magnesia trace 

Carbonic acid trace 

Phosphoric acid trace 

Chlorine ~ trace 

Alkalies , none 

Quartz and insoluble silicates 95.863 

100.000 

Here we note the absence in weighable quantity of 
magnesia and phosphoric acid, while potash could not even 



EEVIEW AND CONCLUSIOISr. 867 

be detected by the tests employed. This soil was mostly 
naked and destitute of vegetation, and its composition 
shows the absence of any crop-producing power. 

Relative Importance of the Ingredients of tlie Soil. 

— From the general point of view of vegetable nutrition, 
all those ingredients of the soil which act as food to the 
plant, are equally important as they are equally indispens- 
able. Absence of any one of the substances which water- 
culture demonstrates must be presented to the roots of a 
plant so that it shall grow, is fatal to the productiveness: 
of a soil. 

Thus regarded, oxide of iron is as important as phos- 
phoric acid, and chlorine (for the crops which require it), 
is no less valuable than potash. Practically, however, 
the relative importance of the nutritive elements is meas-^ 
ured by their comparative abundance. Those which, like 
oxide of iron, are rarely deficient, are for that reason less 
23rominent among the factors of a crop. If any single 
substance, be it phosphoric acid, or sulphuric acid, or pot- 
ash, or magnesia, is lacking in a given soil at a certain 
time, that substance is then and for that soil the most im- 
portant ingredient. From the point of view of natural 
abundance, we may safely state that, on the whole, availa- 
ble nitrogen and phosphoric acid are tlie most important 
ingredients of the soil, and potash, perhaps, takes the next 
rank. These are, most commonly, the substances whose 
absence or deficiency impairs fertility, and are those 
which, when added as fertilizers, produce the most frequent 
and remarkable increase of productiveness. In a multi- 
tude of special cases, however, sulphuric acid or lime, or 
magnesia, assumes the chief prominence, while in many in- 
stances it is scarcely possible to make out a greater crop- 
producing value for one of these substances over several 
others. Again, those ingredients of the soil which could 
be spared for all that they immediately contribute to the 



368 HOW CROPS FEED. 

nourishment of crops, are often the chief factors of fer- 
tility on account of their indirect action, or because they 
supply some necessary physical conditions. Thus humus 
is not in any way essential to the growth of agricultural 
plants, for plants have been raised to full perfection with- 
out it ; yet in the soil it has immense value practically, 
since among other reasons it stores and supplies water and 
assimilable nitrogen. Again, gravel may not be in any 
sense nutritious, yet because it acts as a reservoir of heat 
and promotes drainage it may be one of the most import- 
ant components of a soil. 

What the Soil must Supply. — It is not sufficient that 
the soil contain an adequate amount of the several ash-in- 
gredients of the plant and of nitrogen, but it must be able 
to give these over to the plant in due quantity and pro- 
portion. The chemist could without difficulty compound 
an artificial soil that should include every element of 
plant-food in abundance, and yet be perfectly sterile. The 
potash of feldspar, the phosphoric acid of massive apatite, 
the nitrogen of peat, are nearly innutritions for crops on 
account of their immobility — ^because they are locked up 
in insoluble combinations. 

Indications of Chemical Analysis. — The analyses by 
Baumhauer of soils from the Zuider Zee, p. 862, give in a 
single statement their ultimate composition. We are in- 
formed how much phosphoric acid, potash, magnesia, etc., 
exist in the soil, but get from the analysis no clue to the 
amount of any of these substances which is at the dispo- 
sition of the present crop. Experience demonstrates the 
productiveness of the soil, and experience also shows that 
a soil of such composition is fertile ; but the analysis does 
not necessarily give proof of the fact. A nearer approach 
to providing the data for estimating what a soil may sup- 
ply to crops, is made by ascertaining what it will yield to 
acids. 



EEVIEW .\>7D CONCLUSIpN. 369 

Boussingault has analyzed in this manner a soil from 
Calvario, near Tacunga, in Equador, South America, which 
possesses extraordinary fertility. 

He found its composition to be as follows : 
Nitrogen in organic combination, 0.243 

Nitric acid, 0.975 

Ammonia, 0.010 

Phosphoric acid, ") 0.460 

0.395 

0.023 

traces 



Chlorine, 
Sulphuric acid, 
Carbonic acid, 
Potash and Soda, 
Lime, 
Magnesia, 
Sesquioxide of iron, 



Soluble in acids. ^ , 



1.256 
0.875 
2.450 

Sand, fragments of pumice, and clay insoluble in acids, 83.195 
Moisture, 3.150 

Organic matters (less nitrogen), undetermined substances, 

and loss, 5.938 

100.000 
This analysis is much more complete in reference to ni- 
trogen and its compounds, than those by Baumhauer al- 
ready given (p. 362), and therefore has a peculiar value. 
As regards the other ingredients, we observe that phos- 
phoric acid is present in about the same proportion ; lime, 
alkalies, sulphuric acid, and chlorine, are less abundant, 
while magnesia is more abundant than in the soils from 
Zuider Zee. 

The method of analysis is a guarantee that the one per 
cent of potash and soda does not exist in the insoluble 
form of feldspar. Boussingault found fragments of pumice 
by a microscopic examination. This rock is vesicular feld- 
spar, or has at least a composition similar to feldspar, and 
the same insolubility in acids. 

The inert nitrogen of the humus is discriminated from 
that which in the state of nitric acid is doubtless all assim- 
ilable, and that which, as ammonia, is probably so for the 
most part. The comparative solubility of the two per 
cent of lime and magnesia is also indicated by the analysis. 
16* 



o70 now CROPS FEED. 

Boussingault does not state the kind or concentration, 
or temperature of the acid employed to extract the soil 
for the above analysis. These are by no means points of 
indifference. . Grouven {Iter <b Ster Salzmilnder JBerichte) 
has extracted the same earth with hydrochloric acid, con- 
centrated and dilute, hot and cold, with greatly different 
results as was to be anticipated. In 1862, a sample from 
an experimental field at Salzmiinde was treated, after be- 
ing heated to redness, with boiling concentrated acid for 
3 hours. In 1867 a sample was taken from a field 1,000 
paces distant from the former, one portion of it was treat- 
ed with boiling dilute acid (1 of concentrated acid to 20 
of water) for 3 hours. Another portion was digested for 
three days with the same dilute acid, but without applica- 
tion of heat. In each case the same substances were ex- 
tracted, but the quantities taken up were less, as the acid 
was weaker, or acted at a lower temperature. The follow- 
ing statement shows the composition of each extract, cal- 
culated on 100 parts of the soil. 

EXTRACT OF SOIL OF SALZMUNDE. 

Hot strong acid. 
Potash, .635 

Soda, .127 

Lime, 1.677 

Magnesia, .687 

Oxide of iron and alnmina, 7.931 
Oxide of manganese, .030 

Sulphuric acid, .059 

Phosphoric acid, .059 

Silica, 1.785 

Total, 12.990 

The most interesting fact brought out by the above fig- 
ures, is that strong and weak acids do not act on all the 
ingredients with the same relative power. Comparing the 
quantities found in the extract by cold dilute acid with 
those which the hot dilute acid took up, we find \hat the 
latter dissolved 5 times as much of oxide of iron and 
^ilumina, 4 times as much potash, 3 times as much soda, 



dilute acid. 


Cold dilute add. 


.116 


.029 


.067 


.020 


1.046 


1.098 


.539 


.237 


3.180 


.660 


.086 


.071 


.039 


.020 


.091 


.057 


.234 


.175 


5.398 


2.357 



REVIEW AND CONCLUSION. 371 

twice the amount of magnesia, sulphuric acid, and phos- 
phoric acid, and the same quantity of lime. These facts 
show how very far chemical analysis in its present state 
is from being able to say definitely what any given soil 
can supply to crops, although we owe nearly all our pre- 
cise knowledge of vegetable nutrition directly or indi- 
rectly to this art. 

The solvent effect of water on the soil, and the direct 
action of roots, have been already discussed (pp. 309 to 
328). It is unquestionably the fact that acids, like pure 
water in Ulbricht's experiments (p. 324), dissolve the 
mor€ the longer they are in contact with a soil, and it is 
evident that the question : How much a particular soil is 
able to give to crops ? is one for which we not only have 
no chemical answer at the present, but one that for many 
years, and, perhaps, always can be answ^ered only by the 
method of experience — by appealing to the crop and not 
to the soil. Chemical analysis is competent to inform us very 
accurately as to the ultimate composition of the soil, but as 
reo-ards its proximate composition or its chemical consti- 
tution, there remains a vast and difficult Unknown, which 
will yield only to very long and laborious investigation. 

Maintenance of a Supply of Plant-food.— By the recip- 
x^^ocal action of the atmosphere and the soil, the latter 
keeps up its store of available nutritive matters. The 
difficultly soluble silicates slowly yield alkalies, lime, and 
magnesia, in soluble forms ; the sulphides are converted 
into sulphates, and, generally, the minerals of the soil are 
disintegrated and fluxed under the influence of the oxy- 
jren, the water, the carbonic acid, and the nitric acid of 
the air, (pp. 122-135). Again, the atmospheric nitrogen 
is assimilated by the soil in the shape of ammonia, ni- 
trates, and the amide-like matters of humus, (pp. 254-265). 

The rate of disintegration as well as that of nitrifica- 
tion depends in part upon the chemical and physical char- 
acters of the soil, and partly upon temperature and mete- 



372 now ciiors ¥kkd. 

orological conditions. In the tropics, both these processes 
go on more vigorously than in cold climates. 

Every soil has a certain inherent capacity of production 
in general, which is cliicfly governed by its power of sup- 
plying ])lant-f()od, and is designated its " natural strength." 
The rocky hill ranges of the Ilousatonic yield once in 
30 years a crop of wood, the value of which, for a given 
locality and area, is nearly uniform from century to cen- 
tury. Under cultivation, the same uniformity of crop is 
seen when the conditions remain unchanged. Messrs. 
Lawes and Gilbert, in their valuable experiments, have 
obtained from " a soil of not more than average wheat- 
producing quality," without the application of any ma- 
nure, 20 successive crops of wheat, the first of which was 
15 bushels per acre, the last 17^ bushels, and the average 
of all 10|- bushels. (Jour. Boy. Ag. Soc. of Eng., XxV, 
490.) The same investigators also raised barley on the 
same field for 16 years, each year applying the same quan- 
tity and kinds of manure, and obtaining in the first 8 
years (1852-59) an average of 44i bushels of grain and 
28 cwt. of straw ; for the second 8 years an average of 51 §■ 
bushels of grain and 29 cwt. of straw ; and for the 16 
years an average of 48^ bushels .of grain and 28^ cwt. of 
straw. {Jour. ofBathandWestofEng.Ag.8oc.,'XY'i,2U.) 

The wheat experiments show the natural capacity of 
the Rothamstead soil for producing that cereal, and de- 
monstrate that those matters which are annunlly removed 
by a crop of 161- bushels, are here restored to availability 
by weathering and nitrification. The crop is thus a 
measure of one or both of these processes.* It is probable 

♦ In tho experiments of Lawes and Gilbert it was found that phosphates, sul- 
phates, and c.'irlxjiiatcs of linu\ i)()tasli, niiiirnosia, and soda, raised the j)roducc 
of wiieat but 2 to ■'! hiisluls jxr acre ahovi; tlic yield of the unmanured BOil, while 
sulphate and muriate of anuuonia increased tlie crop 6 lo 10 buslicls. This re- 
Bult, obtaiiicd on tliree soils, viz., at Kotliamstead in Herts, Jlolkliam in Nor- 
folk, and Rodmersham in Kt!nt, the experiments extending: over periods of 8, 3, 
and 4 years, respectively, shows that these soils were, for the wheat crop, rela- 
tively deficient in assimilable nitrosren. The crop on the unmamired soil was 
therefore a measure of nitrification rather than of mineral disintegration. 



REVIEW AND COXCLU.SIO.V. 373 

that this native power of producing wheat will last unim- 
paired for years, or, perhaps, centuries, provided the depth 
of the soil is sufficient. In time, however, the silicates 
and other compounds Avhose disintegration supplies alka- 
lies, phosphates, etc., must become relatively less in quan- 
tity compared with the quite inert quartz and alumina- 
silicates which cannot in any way feed plants. Then the 
crop will fall off, and ultimately, if sufficient time he al- 
lowed, the soil will he reduced to sterility. 

Other things being equal, this natural and durable pro- 
ductive power is of course greatest in those soils which 
contain and annually supply the largest proportions of 
plant-food from their entire mass, those which to the great- 
est extent originated from good soil-making materials. 

Soils formed from nearly pure quartz, f]-om mere chalk, 
or from serpentine (silicate of magnesia), are among those 
least capable of maintaining a supply of food to crops. 
These poor soils are often indeed fairly productive for a 
i^w years when first cleared from the forests or marshes; 
but this temporary fertility is due to a natural manuring, 
the accumulation of vegetable remains on the surface, 
which contains but enough nutriment for a few crops and 
wastes rapidly under tillage. 

Exhaustion of the Soil in the language of Practice has 
a relative meaning, and signifies a reduction of producing 
power below the point of remuneration. A soil is said to 
be exhausted when the cost of cropping it is more than 
the crops are worth. In this sense the idea is very indef- 
inite since a soil may refuse to grow one crop and yet may 
give good returns of another, and because a crop that re- 
munerates in the vicinity of active demand for it, may be 
worthless at a little distance, on account of difficulties of 
transportation. The speedy and absolute exhaustion of a 
soil once fertile, that has been so much discussed by spec- 
ulative writers, is found in their writings only, and does 
not exist in agriculture. A soil may be cropped below the 



374 HOW CRors feed. 

point of remuneration, but the sterility thus induced is of 
a kind that easily yields to rest or other meliorating agen- 
cies, and is far from resembling in its permanence that 
which depends upon original poverty of constitution. 

Significance of the Absorptive Quality. — Disintegration 
and nitrification would lead to a waste of the resources 
of fertility, wer6 it not for the conserving effect of those 
physical absorptions and chemical combinations and re- 
j^lacements which have been described. The two least 
abundant ash-ingredients, viz., potash and phosphoric acid, 
if liberated by the weathering of the soil in the form of 
phosphate of potash, would suffer speedy removal did not 
the soil itself fix them both in combinations, which are at 
once so soluble that, while they best serve as plant-food, 
they cannot ordinarily accumulate in quantities destruct- 
ive to vegetation, and so insoluble that the rain-fall cannot 
wash them off into the ocean. 

The salts that are abundant in springs, rivers, and seas, 
are naturally enough those for which the soil has the least 
retention, viz., nitrates, carbonates, sulphates, and hydro- 
chlorates of lime and soda. 

The constituents of these salts are either required by 
vegetation in but small quantities as is the case with chlo- 
rine and soda, or they are generally speaking, abundant 
or abundantly formed in the soil, so that their removal 
does not immediately threaten the loss of productiveness. 
In fact, these more abundant matters aid in putting into 
circulation the scarcer and less soluble ingredients of 
crops, in accordance with the general law established by 
the researches of Way, Eichhorn, and others, to the effect 
that any base brought into the soil in form of a freely sol- 
uble salt, enters somewhat into nearly insoluble combina- 
tion and liberates a corresponding quantity of other bases. 

" The great beneficent law regulating these absorptions 
appears to admit of the following expression : those bodies 
which are most rare and precious to the growing plant are 



EEVIEW AND CONCLUSION. 375 

by the soil converted into^ and retained in, a condition not 
of absolute, hut of relative insoluhility , and are kept avail- 
able to the plant by the continual circulation in the soil 
of the more abundant saline matters. 

" The soil (speaking in the widest sense) is then not only 
the ultimate exhaustless source of mineral (fixed) food, 
to vegetation, but it is the storehouse and conservatory 
of this food, protecting its own resources from waste and 
from too rapid use, and converting the highly soluble 
matters of animal exuviae as well as of artificial refuse 
(manures) into permanent supplies."* 

By absorption as well as by nitrification the soil acts 
therefore to prepare the food of the plant, and to present 
it in due kind and quantity. 

* The author quotes here the conduding paragraphs of an article by him " On 
Some points of Agricultural Science," from the American Journal of Science and 
Arts, May, 1859, (p. 85), which have historic interest in being, so far as he is 
aware, the earliest, broad and accurate generalization on record, of the facts of 
soil-absorption. 

NOTICE TO TEACHERS. 

At the Aiitbor's request, Mr. Louis Stadtmuller, of New Haven, 
Conn., will undertake to furnish collections of the minerals and rocks 
which chiefly compose soils (see pp. 108-122), suitable for study and 
illustration, as also the apparatus and materials needful for the chemical 
experiments described in "How Crops Grow." 



HOW CROPS GROW. 

A. TBEA.TISE 

Ofl tie Chemcal CoiDOSitioii, Structure, ani Life of the Plant, 

FOR ALL STUDENTS OF AGRICULTURE. 

WITH NUMEROUS ILLUSTRATIONS AND TABLES OF ANALYSES. 

BY 

SAMUEL. W. JOHNSON, M.A., 

FBOrESSOR OB" ANALYTICAL AND AGRICULTURAL CHEMISTRY IN YALE COLLEGE ; 

CHEMIST TO THE CONNECTICUT STATE AGRICULTURAL SOCIETY; 

MEMBER OF THE NATIONAL ACADEMY OF SCIENCES. 

TMs is a volume of nearly 400 pages, in which Agricultural 
Plants, or " Crops," are considered from three distinct, yet closely 
related, stand-points, as indicated by the descriptive title. 

THE CHEMICAL COMPOSITION OF THE PLiNT. 

Ut.—The Volatile Part. 

2d. — The Ash — Its Ingredients ; their Distribution, Variation, and 
Quantities, The Composition of the Ash of various Farm 
Crops, with full Tables ; and the Functions of the Ash. 

3d. — Composition of the Plant in various Stages of Growth, and the 
Relations subsisting among the Ingredients. 

THE STRUCTURE OF THE PLANT AND THE OFFICES 
OF ITS ORGANS. 

T/ie Primary Elements of Organic Structure. 

The Vegetative Organs — ^Root, Stem, and Leaf, and their Funo- ' 
tions ; and 

The Beproductive Organs, namely, Flowers and Fruit, and the 
Vitality of Seeds with their Influence on the Plants they produce. 

THE LIFE OF THE PLANT. 

Germination, and the conditions most favorable and unfavor- 
able to it. 

The Food of the Plant when independent of the Seed. 

Sap and its Motions, etc., etc. 

The Appendix, which consists of twelve Tables exhibiting^ 
the Composition of a great number of Plants viewed from many 
different stand-points, will be found of inestimable value to practi 
oal afifriculturists, students, and theorists. 

BENT POST-PAID. PRICE, $2. 

ORANGE JUDD & CO., 

245 Broadway, New-York. 

3477 4 



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